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SAUNDERS'   QUESTION-COMPENDS.    No.  t. 

ESSENTIALS 


OF 


PHYSIOLOGY 

PREPARED   ESPECIALLY   FOR 

STUDENTS  OF  MEDICINE 


BY 

SIDNEY  P.  BUDGETT,  M.D. 

1 1 

Professor  of  Physiology  in  the  Medical  Department  of  Washington  University, 

St.  Louis. 


Second   Edition,    Thoroughly   Revised 

BY 

HAVEN  EMERSON,  A.M.,  M.D. 

i  "t  Physiology  in  Columbia  University  (College  of  Physicians  and 
Surgeons),  New  York. 

x 
ARRANGED  WITH  QUESTIONS  FOLLOWING  EACH  CHAPTER 


ILLUSTRATED 


PHILADELPHIA    AND    LONDON 

.  B.  SAUNDERS    COMPANY 

1906 


''•'..CQf     '* 


;  -S^fciip,  iele(Jtrt>ty]?ed',  »print«?d,  and  copyrighted  November,  1901. 

Reprinted  October,  1902. 
Revised,  reprinted,  and  recopyrighted  August,  1905. 


COPYRIGHT,  1905,  BY  W.  B.  SAUNDERS  &  COMPANY. 


Reprinted  August,  1906. 


PRESS  OF 

W.  B.  SAUNDERS  COMPANY 
PHILADELPHIA 


PREFACE  TO  THE  SECOND  EDITION. 


Tin:  present  revision  has  given  opportunity  to  add  a 
short  summary  of  the  adaptations  of  the  blood  in  health 
and  disease  to  foreign  substances  introduced  into  the 
body.  A  somewhat  fuller  treatment  of  the  subject  of 
human  lactation  and  of  the  functions  of  the  red  and 
white  blood-cells  and  of  the  blood  as  a  tissue  has 
seemed  advisable.  No  change  in  the  scope  of  the  book 
JIMS  l>een  attempted. 

HAVEN  EMERSON. 
Ni:\v  YORK. 


'723*3 


PREFACE. 


THESE  abbreviated  lecture  notes  are  intended  for 
the  use  of  students  in  conjunction  with  a  text-book, 
and  not  as  a  substitute  for  a  larger  work.  Conse- 
quently, no  attempt  has  been  made  fully  to  illustrate 
this  book.  The  questions  introduced  at  the  end  of 
eaeh  chapter  are  not  exhaustive,  but  may,  it  is  hoped, 
if  carefully  considered,  be  found  useful  as  an  aid  to 
thinking  over  what  has  been  read. 


CONTENTS. 


CHAPTER  I.  PAOE 

Protoplasm,  Blood,  and  Lymph 11 

CHAPTER  II. 
The  Circulation  of  the  Blood      39 

CHAPTER  III. 
Respiration      63 

CHAPTER  IV. 
Digestion ...... 77 

CHAPTER  V. 
Metalx>lism  and  Nutrition 105 

CHAPTER  VI. 
Excretion 127 

CHAPTER  VII. 
Animal  Heat 141 

CHAPTER  VIII. 
Muscle  and  Nerve 147 

CHAPTER  IX. 
The  Nervous  System     .   . . 160 

CHAPTER  X. 
The  Special  Senses .210 


Index .229 


PHYSIOLOGY. 


CHAPTER  I. 

PROTOPLASM,  BLOOD,  AND  LYMPH. 

PROTOPLASM. 
PHYSIOLOGY  is  the  science  of  the  functions  of  living 

matter,  as  distinguished  from  the  science  of  the  form 
of  living  matter,  or  Morphology.  The  two  groups  <>f 
living  matter  are  plants  and  animals,  which  are  distin- 
guished physiologically  bv  the  following  essential  differ- 
ence : 

The  plant  is  able  by  the  aid  of  solar  energy  to  con- 
.-trnei  its  protoplasm  from  inorganic  matter,  t.  e.,  water, 
carbon  dioxid,  and  inorganic  salts.  The  animal  cell  is 
unable  to  form  protcid  material  from  inorganic  mate- 
rial. The  animal  cell  has  feeble  powers  <>!'  synthesis 
and  i>  characterized  chiefly  by  its  power  to  break  down 
organic  material  into  simpler  compounds.  The  animal 
cell  must  make  its  protoplasm  largely  of  organic  com- 
pounds alreadv  formed. 

Living  protoplasm,  or  bioplasm,  is  composed  of  a 
fine  network  of  fibrilhe  in  which  the  more  fluid  portion 
of  the  protoplasm  is  contained.  Protoplasm  is  impo-- 
>ible  .if  exact  analysis  since  its  life  is  destroyed  by 
treatment  with  chemical  reagents.  It  contains  a  large 

11 


12     \:  fj  PROTOPLASM,  BLOOD,  AND  LYMPH. 


st->i<  v:f  pme'itiai  c.ie;;«r\  ;  it  is  unstable;  and  has  the 
following  propei  -ties  :  iri  liability,  contractility,  con- 
ductivity, nutrition,  or  assimilation,  including 
processes  of  construction  and  destruction,  and  repro- 
duction. 

By  irritability  is  meant  that  property  of  proto- 
plasm by  virtue  of  which  it  is  able  to  respond  to  a 
stimulus,  which  may  be  the  normal  nerve-impulse  — 
probably  consisting  in  the  transmission  of  a  physical 
rather  than  a  chemical  change  along  a  nerve  fiber  —  or 
an  artificial  stimulus,  mechanical,  thermal,  chemical, 
or  electrical.  The  response  consists  of  a  chemical 
change  in  the  protoplasm,  accompanied  by  the  produc- 
tion of  heat  or  visible  motion  or  both,  and  often  to  a 
degree  far  in  excess  of  the  energy  applied  as  a  stimulus. 

Contractility  is  the  property  by  virtue  of  which 
protoplasm  is  able  to  change  its  shape;  the  simplest 
instance  being  the  ameboid  movement  of  the  white 
blood-cells. 

Conductivity  is  the  property  by  virtue  of  which 
protoplasm  is  able  to  transmit  an  impulse  from  one 
part  to  another  of  its  substance,  as  instanced  in  the 
passage  of  a  nerve  impulse. 

By  nutrition  we  mean  the  power  of  converting  dead 
food  material  into  living  substance. 

By  reproduction  we  mean  the  power  of  each  cell,  or 
organism,  to  perpetuate  its  kind  by  the  formation  of 
new  individuals. 

The  tissues  of  the  human  body  consist  of  cells  and 
intercellular  substance,  the  latter  being  of  simpler 
material  than  the  protoplasm  of  the  cells,  manufactured 
by  the  cells,  and  lacking  the  characteristics  of  living 
matter. 

On  analysis,  dead  protoplasm  is  found  to  consist  of 
water,  inorganic  salts,  proteids,  nucleoproteids,  carbohy- 


1'KOTEJDS.  13 

(1  rates,  fats,  lecithin,  cholesterin,  and  various  simpler 
substances.  Whether,  and  to  what  extent,  these  are,  in 
the  living  condition,  chemically  combined  with  one  an- 
other is  not  known. 

Proteids  are  highly  complex  bodies  of  unknown 
composition,  made  up  of  carbon,  oxygen,  hydrogen, 
nitrogen,  sulphur,  and  sometimes  phosphorus,  in  the  fol- 
lowing proportions  by  weight:  Carbon,  51  to  55%  ; 
Oxygen,  20  to  24%  ;  Nitrogen,  15  to  17%  ;  Hydro- 
gen,  6.8  to  7.3%  ;  and  Sulphur,  0.3  to  5%.  A  single 
proteid  molecule  may  perhaps  contain  as  many  as  2000 
atoms;  the  molecular  weight  of  egg-albumen  being 
possibly  as  high  as  14,000.  Native  proteids  are  coagu- 
lated by  boiling;  they  are  precipitated  by  alcohol,  by 
the  salts  of  the  heavy  metals,  and  by  mineral  acids,  and 
are  coagulated  by  prolonged  treatment  with  alcohol; 
they  are  nondialv/able.  The  table  on  the  following  page 
gives  the  solubility  of  several  native  proteids,  proteoses, 
and  peptones. 

Nucleoproteids  are  the  most  abundant  proteids 
found  in  the  cell  protoplasm.  They  are  compounds 
of  a  proteid  and  nuclein,  nuclein  itself  being  a  com- 
pound of  a  proteid  and  nucleic  acid,  while  nucleic  acid 
may  be  split  into  phosphoric  acid  and  nucleic  bases, 
Mich  as  adenin,  guanin,  etc. 

Carbohydrates  are  composed  of  carbon,  hydrogen, 
and  oxygen,  the  two  latter  being  present  in  the  propor- 
tions to  form  water;  they  are  simpler  than  the  proteids, 
though  some  of  the  polysaccharids  appear  to  be  very 
complicated  in  structure  : 

The  carbohydrates  may  be  divided  into  three  groups, 
as  follows : 

Monosaccharids,  e.  </.,  Grape-sugar,  CGH12O6. 
Disaccliarids,  c.  (/.,  ( 'anc-sngar,  CjjHjjOjj. 
Polysaccharids,  c.  ^/.,  [Starch,  (CtiH10O5)n. 


14 


PROTOPLASM,   BLOOD,   AND  LYMPH. 


%                 UW         ^    0            ^    V    >    H 

g      |l   II    I  £f  i 
§      II   11    II  1  1 

co    cc                                              y 

CD                     •                                                   CC 

»—  1                                   M    1—  1 

GO               GO    B          GO                 B     B    GO 

O                  C     "/I           O                   cc     7)     o 

1 

SOLUBILITY. 

GO                GO   GO         GO                 GO   GO   GO 

o 

P 

NaCl  SOLUTION. 

g                g   g         g                 1*   g   g 

5  ce 

GO                ^    S     o  ^                  loco00 

Saturated. 

22  >-                   HH  w  h- 

GO          co  ,Jg-    B          B                  B     B     B 

O           o  -vi   co          co                 co    cc    co 
>—  i           H—  '  ^    o                                O     O     O 

Saturated 

+  acid. 

tT1    hH            1—  1                       h-  1    1—  f    1—  I 

GO               g     3          B                  B     B     B 
O                 g     co          cc                  co     co     cc 
j—  "                &  O 

(NH4)2S04. 
Saturated  Sol. 

t—  1    1—  1    hH 

GO               GO   GO    •     GO                 B     B     B 
O     O          O                  cc     co     co 

II 

PROTEIDS.  15 

The  stereochemical  formulae  of  many  sugars  are 
kno\\  n,  Kmil  Fischer  having,  in  the  laboratory,  syn- 
thesized a  greater  number  than  are  known  to  exist  in 
nature.  The  monosaccharids  are  aldehyds  or  ketones 
of  hexatomic  alcohols,  and  are  known  as  aldoses  and 
ketoses  ;  for  instance,  dextrose  is  the  aldehyd  of  the 
alcohol  sorbite  ;  levulose,  or  fruit-sugar,  is  the  ketone 
of  the  alcohol  inannite. 

The  stereoelieniical  formula  for  Grape-sugar  (d-Glu- 
cose,  or  Dextrose)  is  as  follows  : 

H    II  OH   H 

I      I      I      I 
CH2OH  -  C— C-C— C— COH 

I      I      I      I 
OH  OH  H  OH 

For  Fruit-sugar  (d-Levulose)  : 

H    H  OH 

I      I      I 
CH2OH— C— C— C— CO— CHaOH 

I      I      I 
OH  OH  H 

In  the  formula  for  dextrose,  it  will  be  notieed  that 
there  are  a  number  of  possible  different  arrangements 
of  the  four  intermediate  (1II.()II  groups;  for  instance, 
We  may  transpose  the  II  and  the  OH  in  the  last  group, 
thus  : 

H    H  OH  OH 

I      I      I      I 
CH,OH-C— C— C-  C— COH 

I      I      I      I 
OH  OH  H  H 

and  we  have  d-Mannose,  another  sugar  of  the  aldose 
group.  It  would  be  possible  for  sixteen  different  al- 
doses  to  exist,  each  with  the  formula  CH,OH.(CHOH)r 
<  '<  >Il  ;  of  these,  twelve  are  known.  Like  other  aide- 


16  PROTOPLASM,   BLOOD,  AND  LYMPH. 

hyds,  they  act  as  reducing  agents,  upon  which  property 
depend  Trommer's  and  Fehl ing's  tests. 

A  series  of  these  glycoses  has  been  investigated,  be- 
ginning with  Triose ;  in  the  triose  group  there  are  two 
possible  isomers,  only  one,  Glycerose,  being  known. 
The  series  is  as  follows  : 

Trioses,  C3H,.O3.  2  possible  isomers. 

Tetroses,  C4H8O4.  4  «  " 

Pentoses,  C5H10O5.  8  "  " 

Hexoses,  C6H12O6.  16  t(  " 

Heptoses,  C7HUO7.  32  « 

Octoses,  C8H16O8.  64  «  « 

Nonoses,  C9H18O9.  128  « 

Only  those  containing  three  carbon  atoms,  or  a  multiple 
of  three, — namely,  members  of  the  triose,  hexose,  and 
nonose  groups, — are  assimilable  to  more  than  a  trifling 
extent ;  the  others,  when  absorbed  from  the  alimentary 
canal,  being  excreted  unchanged  by  the  kidneys. 

Of  the  disaccharids,  the  three  following  are  of  in- 
terest :  Cane-sugar,  Malt-sugar,  and  Milk-sugar.  Cane- 
sugar  can,  by  hydrolysis  (see  below),  be  converted  into 
one  molecule  of  dextrose  and  one  molecule  of  levulose  ; 
Malt-sugar,  or  Maltose,  into  two  molecules  of  dextrose ; 
and  Milk-sugar,  or  Lactose,  into  one  molecule  of  dex- 
trose, and  one  molecule  of  galactose,  another  member 
of  the  hexose  group. 

Of  the  polysaccharids,  starch,  the  dextrins,  glyco- 
gen,  and  cellulose  are  familiar  instances ;  the  formula 
for  each  being  (C6H10O5)n. 

Fats  are  the  ethereal  salts  of  glycerin  and  fatty 
acids ;  animal  fats  usually  being  mixtures  of  the  thre' 
fats: 


METABOLISM.  17 

I'alinitin,  C.H.^CjgH^O.,),.     Melting-point,  45°  C. 
Stearin,     ( '  j  I  (<  \  J  I,'  ()J3.  "  «        53°-66°  C. 

Olein,       CX^H^),.  «  «       -5°C. 

The  melting-point  of  a  mixed  fat  depends  on  the  rela- 
tive proportions  of  the  mixture.  Human  fat  contains 
from  $1  c/o  to  80^  olein,  and  is  liquid  at  body-temper- 
ature. 

Lecithin  is  a  complicated  nitrogen-  and  phosphorus- 
containing  fat,  found  in  all  cells,  and  more  especially  in 
the  nervous  system. 

Cholesterin,  C^H^OH,  is  also  found  in  the  nervous 
system  ;  it  is  a  constituent  of  all  cells,  especially  blood- 
cells,  and  is  present  in  the  bile.  It  is  a  monatomic 
alcohol. 

Of  special  importance,  amongst  the  inorganic  salts 
of  protoplasm,  are  the  phosphates  and  chlorids  of  po- 
ta-sium,  sodium,  and  calcium.  Iron  is  also  present, 
and  is  an  indispensable  constituent  of  the  red  blood- 
cell. 

The  sum  of  the  chemical  exchanges  occurring  in  liv- 
ing tissue  is  known  as  Metabolism.  The  process  of 
building  up  living  tissues,  or  assimilation,  may  be 
spoken  of  as  Anabolism  and  is  constructive  or  syn- 
thetic. Destructive  or  analytic  processes  are  summed 
up  in  the  term  Katabolism.  There  is  never  complete 
<  <  — ation  of  these  processes  even  during  rest  of  tissues 
or  cells.  Equilibrium  is  only  obtained  by  constant 
eliange;  the  constant  destruction  which  goes  on  within 
the  cell  demands  an  equally  continuous  supply  of  new 
material,  which  in  the  case  of  the  proteids  must  be 
-iipplied  as  such  from  without.  Hence  the  name 
proteids,  or  material  "of  first  importance." 

Since  oxidation  is  one  of  the  chemical  changes  in- 
2 


18  PROTOPLASM,  BLOOD,  AND  LYMPH. 

eluded  under  metabolism,  a  continuous  supply  of  oxy- 
gen is  another  necessity.  One  of  the  chief  products 
of  oxidation  is  carbon  dioxid ;  this,  and  other  waste 
products  arising  from  katabolic  changes,  must  be  re- 
moved from  the  cell  as  fast  as  they  are  formed,  as  their 
accumulation  is  injurious  to  the  bioplasm,  and  destruc- 
tive of  its  irritability. 

Another  characteristic  katabolic  change  is  Hydrolysis, 
which  consists  in  the  hydration  and  splitting-up  of  a 
comparatively  complex  substance  into  two  or  more 
simpler  bodies ;  for  instance  : 

(C6H1005)n      +     nH20    =    nC6H1206. 
Glycogen  Water  Dextrose 

Amongst  the  anabolic  or  synthetic  changes  there 
occurs  the  opposite  of  hydrolysis — namely,  one  consist- 
ing of  the  building  of  two  or  more  comparatively 
simple  bodies  into  one  complex  substance,  accompanied 
by  dehydration  ;  for  instance  : 

nC6H1206      =     (C6H1005)n      +     nH20 
Dextrose  Glycogen  Water. 

This  is  called  dehydrolysis. 

After  the  food  has  been  absorbed  by  the  walls  of  the 
alimentary  canal,  it  is  still  far  out  of  the  reach  of  the 
majority  of  the  cells  of  the  body ;  the  same  is  true  of 
the  oxygen  that  is  absorbed  from  the  air  spaces  of  the 
lungs ;  the  cells  would  thus  starve  to  death  but  for  the 
intervention  of  the  Blood,  which,  as  it  passes  through 
the  vessels  of  the  alimentary  canal,  takes  up  the  food, 
and  on  its  way  through  the  pulmonary  vessels,  takes 
up  oxygen,  carrying  these  to  all  parts  of  the  body. 
The  blood  is,  however,  inclosed  in  a  system  of  tubes, 
so  that  only  those  cells  which  line  the  vessels  can 
obtain  their  nourishment  directly  from  the  blood. 


THE  BLOOD.  19 

Through  tin-  walls  of  the  smaller  vessels,  there  filters 
out  a  li(jiiid,  closely  resembling  the  blood  plasma, 
called  Lymph.  In  it,  held  in  solution,  are  the  neces- 
sary food-stiitls,  and  into  it  as  it  lies  in  the  lymph- 
spaces,  which  intervene  between  the  cells  of  the  various 
tissues,  there  diffuses,  from  the  blood-vessels,  oxygen  ; 
BO  i  hat  the  cells  are  thus  supplied  with  both  food  and 
oxygen,  through  the  lymph,  by  the  blood.  At  the 
same  time  the  waste  products  of  cell  metabolism  pass 
from  the  cells  into  the  lymph,  and  thus  to  the  blood,  by 
which  they  are  carried  to  the  various  organs  whose 
i  unction  it  is  to  excrete  them.  The  blood  thus  plays 
the  part  of  both  purveyor  and  scavenger.  It  also 
serves  to  equalize  the  temperature  of  the  different  parts 
of  the  body. 

THE  BLOOD. 

The  blood  consists  of  cells  and  plasma.  In  that  of 
man,  the  cells  form  about  48^  ;  in  that  of  women  and 
children,  rather  less.  The  cells  are  of  two  varieties — 
the  red  cells,  or  erythrocytes ;  and  the  white  cells,  or 
leukocytes.  Of  the  latter,  there  are  several  different 
f<»rms.  In  the  blood  of  man  there  are  about  5,000,000 
red  cells  to  the  cubic  millimeter ;  in  wToman's  blood, 
about  4,500,000.  The  number  of  white  cells  is  very 
variable ;  on  the  average,  there  are  about  10,000  to  the 
cubic  millimeter.  In  addition  to  the  red  and  white 
cells,  there  are  smaller  bodies,  called  platelets,  or  jjfaqucs; 
about  these  very  little  is  known  ;  they  are  more  numer- 
ous than  the  white  cells,  less  so  than  the  red  ;  they  dis- 
integrate rapidly  in  blood  that  is  shed. 

The  functions  of  the  blood  are  as  follows: 

1 .  It  carries  to  the  tissues  food-stuffs,  after  they  have 
been  properly  prepared  by  the  digestive  organs. 

2.  It  transports  to  the  tissues  oxygen  absorbed  from 
the  air  by  the  lungs. 


20  PROTOPLASM,  BLOOD,  AND  LYMPH. 

3.  It  carries  from  the  tissues  various  waste  products 
formed  in  the  processes  of  disassimilation. 

4.  It  is  the  medium  for  the  transmission  of  the  in- 
ternal secretions  of  certain  glands. 

5.  It  aids  in  equalizing  the  temperature  and  water- 
contents  of  the  body. 

6.  It  forms  substances  which  neutralize,  antagonize, 
or  destroy  foreign  substances  which  may  be  introduced 
into  the  organism  (see  pp.  33  and  34). 

The  functions  of  the  red  blood-cells  are  : 

1.  To  carry  oxygen  from  the  lungs  to  the  tissues. 

2.  To  carry  carbon  dioxid  from  the  tissues  to  the 
lungs. 

Composition  of  the  Blood  Plasma. — 

Water 90% 

Inorganic  Salts  (NaCl,  Nn,CO3,  NaHCO3, 
Na2HPO41  NaH2P04,  KC1,  K2SO4,  Ca3- 
(PO4)2,  CaCl2,  etc.) 0.8% 

Dextrose 0.12-0.2% 

Fats      0.2-(1.0)% 

Proteids  : 

Serum-albumin  .    . 4.52% 

Globulins  :  Serum-globulin     ....        3.10% 
Fibrinogen 0.50% 

Urea 0.02% 

Kreatin,  uric  acid,  xanthin  bases,  lec- 
ithin, etc., traces. 

Nucleoproteids  (?). 

Ferments  (diastatic,  glycolytic,  and  steat- 
olytic). 

It  will  be  seen  that  the  plasma  contains  all  the 
necessary  food-stuff's,  proteid,  carbohydrate,  and  fat. 
Water  and  the  inorganic  salts  are  of  equal  importance. 
The  urea,  kreatin,  uric  acid,  etc.,  represent  waste  prod- 
ucts of  proteid  metabolism. 

It  is  absolutely  necessary  that  the  blood  be  alkaline. 
This  is  insured  by  the  presence  of  the  carbonates  of 


COMPOSITION  OF  THE  BLOOD  PLASMA.  21 

sodium,  and  in  case  of  acid-poisoning,  by  the  splitting 
otf'  <>f  ammonia  from  the  proteid  molecules. 

The  Ducleoproteid  found  in  the  liquid  part  of  the 
blood  after  it  is  shed  perhaps  originates  from  the 
leukocytes  after  the  blood  leaves  the  vessels,  and  may 
not  l»c  a  normal  constituent  of  the  plasma.  Ferments 
arc  present  in  small  quantities  only;  a  diantatie  fennent 
is  one  which  converts  starch  into  sugar;  a  glycolytic 
fi'i'inent  splits  up  sugar;  a  stcatolytic  ferment  splits  up 
fats.  * 

The  three  proteids  of  blood  plasma  differ  in  their 
solubility,  as  is  set  forth  in  Table  I.  They  also  differ 
in  the  temperature  at  which  they  coagulate.  Serum- 
all  >umin  coagulates  at  three  different  temperatures:  the 
first  portion  at  72°  to  75°  C. ;  the  second  at  77°  to 
78°  C.  ;  and  the  third  at  83°  to  86°  C.  Serum- 
globulin  coagulates  at  75°  G. ;  Fibrinogen,  at  56°  C. ; 
and  Nucleoproteid,  at  65°  C. 

Coagulation. — A  highly  important  characteristic  of 
blood  is  its  power  of  clotting  when  shed;  were  it  not 
ibr  this,  fatal  hemorrhage  might  result  from  a  very 
trifling  wound.  In  the  class  of  patients  known  as 
"  bleeders"  this  is  the  case;  their  blood  is  lacking  in 
the  power  of  clotting.  The  term  hemophilia  is  applied 
to  this  condition. 

From  three  to  six  minutes  after  human  blood  leaves 
the  blood-vessel,  if  conditions  be  favorable,  it  becomes 
syrupy  in  consistence,  and  later  forms  a  jelly  which  con- 
traets  and  expresses  a  clear  yellow  liquid — the  Serum. 
This  change  depends  upon  the  appearance,  in  the  plasma, 
of  innumerable  fine  fibrils,  which  are  distributed  through- 
out the  whole  mass  of  blood  in  the  form  of  a  close  mesh- 
work.  In  the  interstices  of  this  the  blood-cells  are  en- 
tangled, so  that  they  form  a  part  of  the  clot,  though  not 
an  indispensable  part,  for  plasma  may  be  caused  to  clot 


22  PROTOPLASM,  BLOOD,  AND  LYMPH. 

after  the  complete  removal  of  the  cells,  in  which  case 
the  clot  is  a  light  yellow,  transparent  jelly. 

The  fibrils,  on  the  formation  of  which  clotting  de- 
pends, consist  of  an  almost  insoluble  proteid  which  is 
called  Fibrin.  If  the  blood,  as  it  is  shed,  be  collected 
in  a  vessel  and  whipped  with  a  bundle  of  twigs,  the 
fibrin  fibrils  adhere,  as  fast  as  they  are  formed,  to  the 
whipper,  and  may  thus  be  removed  from  the  blood. 
The  blood  thus  defibrinated  remains  liquid  indefinitely, 
and,  by  its  appearance,  cannot  be  distinguished  from 
normal  blood.  If  the  fibrin  collected  in  this  way  be 
washed  free  from  the  few  blood-cells  which  are  held 
between  its  fibrils,  it  is  found  to  be  a  stringy,  elastic 
substance,  and  gray  in  color. 

In  composition,  serum  is  similar  to  plasma,  save  that 
it  contains  no  fibrinogen ;  in  addition,  it  contains  a  fer- 
ment of  which  mention  will  be  made  below.  We  see, 
then,  that  fibrinogen  disappears  during  the  clotting  of 
blood.  Further,  if  fibrinogen  be  removed  before  the 
blood  has  had  time  to  clot,  clotting  Avill  be  entirely 
prevented ;  thus  fibrinogen  is  necessary  to  the  clotting 
of  blood. 

The  clotting  of  blood  depends  upon  the  conversion 
of  fibrinogen  into  fibrin.  The  next  question  is,  What 
is  the  cause  of  this  conversion  ?  The  clotting  of  blood 
may  be  prevented  by  the  addition  of  a  certain  quantity 
of  a  salt,  such  as  magnesium  sulphate,  the  amount  added 
being  insufficient  to  precipitate  the  proteids  of  the 
plasma.  Blood  so  treated  is  known  as  salted  blood,  and 
from  it,  by  allowing  the  blood-cells  to  settle,  can  be  ob- 
tained salted  plasma,  which  remains  liquid.  Now,  if 
to  salted  plasma  there  be  added  a  small  quantity  of 
blood-serum,  or  a  small  quantity  of  an  extract  made 
from  a  blood  clotythe  salted  plasma  clots  ;  its  fibrinogen 
is  converted  into  fibrin.  The  small  quantity  of  serum 


CLOTTING  OF  BLOOD.  23 

which  is  necessary  indicates  that  the  process  may  de- 
]»«'iid  upon  the  action  of  a  ferment,  or  enzyme. 

Enzymes. — The  following  are  some  of  the  charac- 
teristics of  enzymes,  or  ferments,  a  class  of  bodies  of 
whose  nature  we  are  ignorant,  their  analysis  having,  so 
far,  proved  impossible,  owing  to  the  difficulty  of  sepa- 
rating them  from  impurities,  and  of  obtaining  them  in 
sufficient  quantities. 

Their  activity  does  not  exhaust  or  use  them  up  ;  con- 
sequently— 

A  minute  quantity  of  enzyme  may  cause  the  fermen- 
tation of  an  indefinite  amount  of  fermentable  material. 

The  accumulation  of  the  products  of  fermentation 
interferes  with  their  continued  action. 

Their  action  is  retarded  by  cold. 

There  is  an  optimum  temperature,  at  which  an  en- 
zyme acts  most  rapidly  :  the  optimum  for  those  found 
in  the  human  body  is  about  40°  C. 

They  are  destroyed  by  boiling,  though  in  a  dry  con- 
dition they  may  be  heated  to  a  temperature  of  100°  C. 
without  injury. 

The  activity  of  many  enzymes  is  dependent  on  the 
reaction  of  the  solution  in  which  they  are  present,  a 
neutral  or  slightly  alkaline  reaction  being,most  favor- 
able in  the  majority  of  cases ;  pepsin,  however,  requires 
a  slightly  acid  reaction. 

The  chemical  change  resulting  from  their  action  is 
usually  one  of  hydrolysis.  (See  page  18.)  Maltase, 
however,  while  its  characteristic  action  is  the  conversion 
of  maltose  (malt-sugar),  by  hydrolysis,  into  dextrose, 
can,  if  added  to  a  strong  solution  of  dextrose,  convert  a 
-mall  portion  of  the  latter  into  maltose.  It  is  possible 
that  other  enzymes  are  capable  of  this  reversed  zymolysis, 
and  that  this  affords  an  explanation  of  the  hindering 
of  an  accumulation  of  the  products  of  fermentation. 


24  PROTOPLASM, 'BLOOD,  AND  LYMPH. 

Finely  divided  platinum,  paladium,  and  iridum,  be- 
have, in  some  respects,  as  do  enzymes ;  for  instance, 
they  may,  by  hydrolysis,  invert  cane-sugar — that  is, 
convert  it  into  equal  parts  of  dextrose  and  levulose. 
In  the  decomposition  of  H2O2,  platinum  appears  to  act 
by  contact,  and  not  by  entering  into  the  reaction. 

We  know  no  more  of  the  method  of  action  of  fer- 
ments than  we  know  of  their  composition  ;  amongst 
other  explanations  that  have  been  suggested  are  the  fol- 
lowing ;  according  to  one  of  these  theories,  the  enzyme 
unites  with  the  fermentable  material  to  form  an  unstable 
compound  which  readily  breaks  down  into  the  original 
enzyme,  and  substances  which  are  simpler  and  more 
stable  than  the  original  fermentable  material,  e.g.: 

(1)  Malt-sugar  -f  Enzyme  +  HZ^  —  Substance  x. 

(2)  Substance  x  =  Enzyme  -f  Grape-sugar  -f  Grape-sugar. 

According  to  another  hypothesis,  the  enzyme  is  in  a 
state  of  molecular  movement,  which  is,  by  contact,  im- 
parted to  the  fermentable  material,  renders  it  unstable, 
or  increases  its  instability,  and  thus  causes  it  to  break 
down  into  simpler  and  more  stable  substances.  The 
susceptibility  of  any  substance  to  the  action  of  a  given 
enzyme  depends  upon  its  molecular  structure. 

To  return  to  the  clotting  of  the  blood,  there  are 
other  indications  that  the  process  is  one  of  zymolysis. 
For  instance,  serum  that  has  been  boiled  is  no  longer 
capable  of  causing  salted  blood  or  solutions  of  pure 
fibrinogen  to  clot ;  again,  clotting  is  retarded  by  cold, 
and  hastened  by  keeping  the  blood  at  or  a  little  above 
body-temperature.  It  is  supposed  that  clotting  is  in- 
deed caused  by  an  enzyme,  to  which  the  name  of  fibrin= 
ferment  has  been  given.  This  ferment  probably  origin- 
ates, on  the  shedding  of  blood,  from  the  union  of  a 
nucleoproteid,  derived  from  the  white  blood-cells,  with 


CLOTTING  OF  BLOOD.  25 

calcium.  Clotting  may  be  prevented  by  the  addition 
of  any  substance — e.  g.,  potassium  oxalate  or  soap — 
which  will  cause  the  precipitation  of  the  soluble  calcium 
of  the  plasma.  It  seems  that  contact  with  any  foreign 
>urface  causes  the  white  blood-cells  to  excrete  nucleo- 
protcid  into  the  plasma,  with  the  subsequent  formation 
of  fibrin-ferment;  for  if  blood  be  drawn  directly  into 
oil  through  an  oiled  cannula,  the  formation  of  fibrin- 
frrment  is  very  much  delayed,  apparently  because  the 
leukocytes  are  protected  from  the  injury  to  which,  but 
for  the  oiling  of  the  cannula  and  receptacle,  they  would 
have  been  subjected.  The  prevention  of  coagulation 
by  cooling  the  blood  to  0°  C.  also  depends,  in  part, 
upon  conservation  of  the  leukocytes. 

The  clotting  of  blood  may,  for  the  time  being,  be 
j in-vented  by  the  intravascular  injection  of  albumoses, 
or  of  a  very  small  quantity  of  nucleoproteid ;  the  in- 
jection of  larger  amounts  of  nucleoproteid  causes 
extensive  intravascular  clotting. 

The  lungs  in  some  unknown  way  lessen  the  tendency 
of  the  blood  that  circulates  through  them  to  coagulate, 
while  the  liver  exerts  an  influence  in  the  opposite 
direction. 

Transfusion. — After  severe  hemorrhage  it  is  some- 
times necessary  to  increase  the  bulk  of  the  patient's 
blood  by  the  injection  of  some  liquid,  and  the  choice  of 
this  liquid  is  important.  Since  defibrinated  blood 
always  contains  fibrin-ferment,  it  is  inadvisable  to  in- 
ject the  blood  of  another  person,  even  if  that  person  is 
known  to  be  perfectly  healthy,  and  the  blood  has  been 
whipped  to  prevent  its  coagulation;  the  fibrin-ferment 
contained  in  it  may  cause  intravascular  clotting  of  the 
n  innant  of  the  patient's  own  blood.  The  injection  of 
blood  taken  from  some  other  animal  is  objectionable  for 
the  same  reason,  and  possesses  another  disadvantage — 


26  PROTOPLASM,  BLOOD,  AND  LYMPH. 

namely,  that  the  blood  of  one  species  may  destroy  the 
cells  in  the  blood  of  another  species  with  which  it  is 
mixed ;  this  is  known  as  the  globulicidal  action. 

The  direct  transfusion  of  blood  from  the  vessel  of  one 
patient  into  the  vessel  of  another  is  dangerous,  in  that 
the  leukocytes  may  be  injured  as  they  pass  through  the 
connecting  cannula,  and  thus,  nucleoproteid  being  set 
free,  fibrin-ferment  may  be  formed  and  coagulation  be 
caused.  In  consequence  of  the  difficulties  and  dangers 
of  using  defibrinated  blood  or  direct  transfusion  of 
blood  from  one  human  to  another  recourse  is  usually 
had  to  infusions  of  solutions  of  inorganic  salts,  subcu- 
taneously  or  intravenously.  A  fluid  for  such  purposes 
should  be  a  perfect  solution,  isotonic  with  the  blood ; 
i.  e.,  the  equivalent  of  an  0.85  %  solution  of  sodium 
chlorid,  sterile,  and  heated  to  body  temperature. 

Calcium,  potassium,  and  sodium  salts  should  be  used 
in  about  the  following  proportions  to  have  an  infusion 
fluid  of  most  efficiency:  Calcium  chlorid,  0.026%; 
Potassium  chlorid,  0.035  %;  Sodium  chlorid,  0.75%. 

After  hemorrhage  an  infusion  of  a  saline  solution 
promptly  fills  the  place  of  the  bulk  of  blood  plasma 
lost,  and  the  regeneration  of  red  blood-cells  usually 
follows  rapidly. 

Osmotic  Pressure.  —  Osmosis  is  not  precisely 
understood,  but  the  following  explanation  of  the 
phenomenon,  though  not  free  from  objections,  may  be 
of  service. 

When  a  substance  is  dissolved  in  a  liquid,  it  behaves 
as  though  it  were  a  gas ;  its  molecules  are  in  constant 
motion.  The  outermost  layer  of  liquid  acts  as  a  limit- 
ing membrane,  against  which  the  molecules  of  the  sub- 
stance in  solution  are  continually  striking ;  the  result 
of  these  impacts  is  a  constant  outward  pressure,  just  as 
the  molecules  of  a  gas  inclosed  in  a  vessel  are  continu- 


OSMOTIC  PRESSURE.  27 

nllv  striking  against  the  inner  surface  of  the  vessel  and 
suhjeetinir  it  to  a  pressure.  In  each  case,  the  pressure 
i-  proportional  to  the  number  of  molecules  contained — 
in  the  one  case,  in  a  given  quantity  of  liquid  ;  in  the 
other,  in  a  given  space.  The  larger  the  number  of 
molecules,  the  greater  the  pressure. 

Let  a  vessel  containing  water  be  divided  into  two 
compartments  by  a  loosely  stretched  membrane  of  such 
a  nature  that  water  can  easily  pass  through  it,  while  it 
is  entirely  impermeable  by  albumin.  If,  now,  some 
albumin  be  introduced  into  one  of  the  compartments,  a 
(Fig.  1),  and  be  dissolved,  its  molecules  will  wander 
in  all  directions  through  the  solution,  and  many  of  them 
striking  against  the  membrane,  will  press  it  through  the 
water,  and  cause  it  to  bulge  into  compartment  b  (Fig.  2). 
This  is  possible  only  where  the  membrane  is  permeable 
by  water.  The  albumin  solution  will  have  increased  in 
bulk,  owing  to  the  passage  of  water  through  the  mem- 
brane. 

When  the  membrane  has  become  taut,  the  passage  of 
water  from  b  into  a  will  not  cease,  for  the  albumin 
molecules  are  not  only  striking  against  the  membrane, 
but  against  every  part  of  the  limiting  layer  of  the  solu- 
tion in  a,  including  that  forming  the  upper  surface  of 
the  liquid.  The  tendency  will  be,  then,  to  force  this 
>urface  layer  upward,  and  since  no  such  tendency  exists 
in  1)  (for  the  water  in  6  contains  no  substance  in  solu- 
tion j,  water  will  continue  to  pass  from  6  into  «,  and  the 
level  of  the  liquid  in  a  will  rise,  while  that  of  the  water 
in  b  will  sink  (Fig.  3).  This  will  go  on  until  all  the 
water  has  been  absorbed  by  the  albumin  solution,  or 
until  the  difference  between  the  levels  of  the  two  liquids 
represents  a  hydrostatic  pressure  equal  to  the  osmotic 
pressure  of  the  albumin  solution,  at  which  point  equi- 
librium will  be  established.  A  much  more  convenient 


28  PEOTOPLASM,  BLOOD,  AND  LYMPH. 


-  — /-     t 


3. 


4  I 


OSMOTIC  PRESSURE.  29 

<»f  ascertaining  the  osmotic  pressure  of  a  solu- 
tion is  the  measurement  of  its  freezing-point. 

When  any  substance  is  dissolved  in  water,  the 
I'ree/ing-point  of  the  solution  is  lower  than  that  of 
water;  the  same  is  true  if  some  solvent  other  than 
water  be  used — the  freezing-point  of  the  solution  is 
lower  than  that  of  the  solvent.  The  freezing-point  is 
depressed  in  proportion  to  the  molecular  concentration 
of  tin-  solution,  and,  of  course,  in  proportion  to  its 
osmotic  pressure.  A  depression  of  the  freezing-point 
l>\  L°  C.  indicates  an  osmotic  pressure  of  9,437  mm. 
of  mercury.  If,  then,  we  find  the  freezing-point  of  a 
solution  to  be,  for  example,  — 0.02°  C.,  its  osmotic  pres- 
sure must  be  9437  X  0.02  =  =  188  mm.  Hg. 

In  order  to  make  solutions  of  two  different  sub- 
-tances,  which  shall  be  isotonic  with  one  another,  each 
MI! stance  must  be  dissolved  in  proportion  to  its  molec- 
ular weight,  and  each  solution  made  up,  by  the  addi- 
tion of  water,  to  the  same  bulk.  For  instance,  take 
one  gram-molecule  of  Cane-sugar,  C^H^O^ — that  is, 
•'»  1-  grams  (a  gram-molecule  is  the  molecular  weight  of 
a  Mihstance  expressed  in  grams), — dissolve  it  in  water, 
and  add  water  until  the  solution  measures  1  liter.  A 
solution  of  Grape-sugar,  C6H12O6,  to  be  isotpnic  with 
the  above  solution  of  cane-sugar,  must  be  made  in  the 
same  way,  with  one  gram-molecule,  180  grams,  of  grape- 
sugar.  The  freezing-point  of  each  will  be  — 1.8°  C. ; 
the  nsmotic  pressure,  9437  Xl.8  ==  16,986  mm.  Hg. 

In  the  case  of  an  equimolecular  solution  of  an  elec- 
tiolvte,  however,  the  freezing-point  would  be  lower, 
and  the  osmotic  pressure  higher.  An  electrolyte  is  a 
>ul stance  a  certain  proportion  of  whose  molecules 
undergo  di-- ociation  when  it  is  dissolved  ;  for  instance, 
Sodium  Chlorid  is,  to  a  certain  extent,  dissociated,  on 
solution,  into  Na  and  Cl  ions,  each  ion  behaving,  as  far 


30  PROTOPLASM,  BLOOD,  AND  LYMPH. 

as  osmotic  pressure  is  concerned,  as  though  it  were  a 
molecule.  In  the  case  of  a  salt  like  Mercuric  Chloric!, 
the  molecules  which  become  dissociated  split  up  into 
three  ions,  Hg,  Cl,  and  Cl,  so  that  the  freezing-point 
will  be  depressed  still  further,  and  the  osmotic  pressure 
will  be  still  higher,  than  in  the  case  of  an  equimolecular 
solution  of  a  nonelectrolyte.  Solutions  of  an  electro- 
lyte are  capable  of  conducting  electricity  ;  solutions  of 
nonelectrolytes  are  nonconductors. 

If  solutions  of  two  different  substances  be  separated 
from  one  another  by  a  membrane  which  is  impermeable 
by  each  of  these  substances,  but  permeable  by  water, 
water  will  pass  through  the  membrane  toward  the 
solution  possessing  the  higher  osmotic  pressure.  This 
wrill  continue  until,  by  the  dilution  of  the  one,  and  con- 
centration of  the  other,  the  osmotic  pressures  of  the  two 
have  been  equalized ;  that  is,  provided  the  two  liquids 
be  kept  at  the  same  level,  in  order  to  exclude  the  effect 
of  hydrostatic  pressure. 

If  solutions  of  two  different  substances  be  separated 
from  one  another  by  a  membrane  which  is  impermeable 
by  one  of  them,  slightly  permeable  by  the  other,  and 
readily  permeable  by  water,  the  result  may  be  compli- 
cated. As  an  example,  let  us  take  two  solutions,  a  and 
6,  separated  by  a  membrane  which  is  impermeable  by 
the  substance  dissolved  in  a,  slightly  permeable  by  the 
substance  dissolved  in  b,  and  readily  permeable  by 
water.  If  the  osmotic  pressure  of  a  be  greater  than 
that  of  6,  water  will  pass  from  b  to  a,  but  not  so 
rapidly  as  it  would  do  if  b  were  pure  water ;  for  the 
osmotic  pressure  of  6  will  retard  its  loss  of  water,  since 
the  majority  of  the  molecules  in  b  will,  on  reaching  the 
membrane,  strike  against  it  and  rebound  ;  a  few  will, 
however,  pass  through  into  a,  and  the  final  result,  if 
the  experiment  be  sufficiently  long  continued,  will  be 
the  complete  absorption  of  6  by  a. 


ERYTHROCYTES.  31 

If,  at  the  beginning  of  the  experiment,  the  osmotic 
piv-sure  of  l>  he  greater  than  that  of  a,  although  the 
final  result  will  be  the  same  as  in  the  last  case  con- 
sidered, water  will  at  first  pass  from  a  to  6,  for  more 
I  mil  is  exerted  by  b.  Since,  however,  the  osmotic 
pn-sure  of  b  will  be  continually  reduced,  not  only  by 
dilution,  but  also  by  the  slow  diffusion  of  its  dissolved 
substanee  into  a,  and  at  the  same  time  the  osmotic 
pressure  of  (i  will  continually  increase,  owing  to  loss  of 
water  and  gain  of  the  substance  which  diffuses  into  it 
t'miu  b,  a  time  must  come  when  the  two  solutions  are 
isotonic  with  one  another,  and  the  passage  of  water 
through  the  membrane  will  momentarily  cease.  The 
-ult-tanee  dissolved  in  b  will,  however,  continue  to 
diffuse  through  the  membrane  into  a;  this  will  raise 
the  osmotic  pressure  of  a  above  that  of  6,  and  water 
will  now  begin  to  pass  in  the  direction  of  a.  The  final 
re-ult  will,  as  above,  be  the  complete  absorption  of  b 
by  a. 

Erythrocytes. — The  chemical  composition  of  the 
iv  1  cells  is  about  as  follows  : 

Water 90.0%. 

Hemoglobin 36.0%. 

Proteids 3.2%. 

Lecithin  and  cholesterin 0.2%. 

Inorganic  salts 0.6^. 

While  amongst  the  inorganic  salts  of  plasma  and  lymph 
the  sodium  salts  predominate,  in  the  cells  potassium 
silts  are  the  more  abundant. 

Hemoglobin  is  a  compound  proteid,  which  may  be 
split  up  into  a  globulin  and  a  pigment,  Hemochromogen. 
Both  these  substances,  apparently  owing  to  the  fact  that 
tin  y  contain  iron,  possess  a  marked  affinity  for  oxygen, 
with  which  they  unite  to  form  unstable  compounds;  in 
the  one  case  Oxy hemoglobin,  in  the  other,  Hematin. 
Hemoglobin,  Hb,  and  Oxyhemoglobin,  HbCXj,  are  both 


32  PROTOPLASM,   BLOOD,  AND  LYMPH. 

crystalline,  and  soluble  in  water.     Oxyhemoglobin  is 
scarlet  in  color,  and  is  accountable  for  the  color  of  arte-  i 
rial  blood,  venous  blood  being  dark  purple  owing  to  the 
reduction  of  much  of  the  hemoglobin.     Hemoglobin 
also  possesses  an   affinity  for  Carbon    monoxid,  with  i 
which  it  unites  to  form  Carbon-monoxid  hemoglobin, 
HbCO,  a  compound  which  is  more  stable  than  HbO2.  j 
This  is  why  the  inhalation  of  coal-gas  is  dangerous ;  ; 
the  carbon  monoxid  contained  in  coal-gas  combines  with 
the  hemoglobin,  and  thus  prevents  its  union  with  oxy- 
gen.    Hemoglobin  forms  a  still  more  stable  compound 
with  nitric  oxid.     If  oxyhemoglobin  be  treated  with  an  i 
oxidizing   agent,  it   is  converted    into    Methemoylobin, 
which  contains  the  same  amount  of   oxygen  as  does 
oxyhemoglobin,  but  the  union  is  a  firmer  one.    Methem- 
oglobin  is  brown  in  color.     Each  of  these  pigments 
shows,  in    dilute   solution,  a    characteristic    spectrum. 
Oxyhemoglobin  shows  two  absorption  bands  between 
the  Frauenhofer  lines  D  and  E,  the  band  toward  the 
red  end  of  the  spectrum  being  the  narrower  and  darker 
of  the  two.     Reduced  hemoglobin  shows  one  band,  be- 
tween the  lines  D  and  E,  which  is  broader  and  less 
well-defined  than  the  absorption  bands  of  oxyhemoglo- 
bin.    By  means  of   photography,  another   absorption 
band,  still  more  characteristic  of  blood  pigment,  may 
be  shown  between  the  Frauenhofer  lines  G  and  II 
this  is  known  as  Soret's  band. 

Leukocytes,  or  white  blood-cells,  are  composed 
about  as  follows  :  Water,  88.5  Cf0  ;  proteids  and  nucleo 
proteids,  9  ^  ;  and  small  quantities  of  lecithin,  choles- 
terin,  fats,  inorganic  salts,  etc. 

The  leukocytes  are,  as  we  have  seen,  concerned  in 
the  clotting  of  blood ;  the  blood  platelets  also  probably 
take  part  in  the  formation  of  fibrin-ferment.  The  leu- 
kocytes possess  the  power  of  changing  their  shape  (ame- 


ADAPTATION  OF  BLOOD.  33 

boid  vemcnt),  and  in  this  way  escape  through  the 

walls  of  the  capillary  blood-vessels  (diapedesis)  and 
wander  through  the  tissue  spaces  ;  this  process  is  greatly 
accelerated  by  the  presence  of  an  irritant,  the  leukocytes 
collecting  in  large  numbers  in  an  inflamed  area,  and 
being  directed  thither  by  chemotropism.  If  a  small 
tube  filled  with  a  culture  of  bacteria  be  introduced 
under  the  skin,  the  chemical  products  of  bacterial  ac- 
tivity will  diffuse  through  the  open  end  of  the  tube  into 
the  lymph-spaces;  on  coming  in  contact  with  the  leu- 
kocyte-, they  influence  them  in  such  a  manner  that  the 
leukocytes  are  caused  to  move  in  the  direction  from 
which  the  bacterial  products  approach  them.  It  is  sup- 
po-cd  that  the  leukocytes  either  ingest  the  bacteria 
( phagocytosis),  or  secrete  some  substance  which  inhibits 
their  growth  and  activity;  the  leukocytes  of  the  frog 
have  been  shown  to  do  both,  In  this  way  the  white 
blood-cells  may  afford  protection  against  the  inroads  of 
bacteria, .and  assist  in  maintaining  the  health  of  the 
Individual. 

The  functions  of  the  leukocytes  are : 

1.  To  protect  the  body  against  pathogenic  bacteria 
(phagocytic  and  bactericidal  action). 

_.   To  aid  in  the  absorption  of  fats  from  the  intestine. 

•  >.  To  aid  in  the  absorption  of  peptones  from  the  in- 
testine. 

4.  To  take  part  in  the  process  of  blood-coagulation. 

:>.  To  help  maintain  the  normal  composition  of  the 
blood  plasma  as  to  proteids. 

ADAPTATION  OF  BLOOD. 

Kmler  the   description   of  blood  and   its   functions 

should   be  included  the  chemical  defenses  of  the  l»«.dv 

against  injury  and  disease.     C1lotting  of  blood  is  a  great 

protection  against  injury.     The  acid  gastric  juice  is  de- 

3 


34  PROTOPLASM,  BLOOD,  AND  LYMPH. 

structive  to  most  bacteria  introduced  in  the  food.  But 
in  addition  to  these  means  of  assisting  in  the  protection 
of  the  body,  there  is  a  power  of  adaptation  to  meet  the 
harmful  agencies  which  may  enter  the  blood  stream, 
possessed  by  the  blood  plasma,  and  capable  of  great 
development  and  apparently  of  innumerable  variations. 
The  presence  of  these  substances  in  the  plasma  is  due 
chiefly  to  the  activity  of  the  endothelial  cells  lining  the 
heart  cavities  and  the  blood  vessels,  and  of  the  red  and 
white  blood-cells. 

Bacteriolysins  are  soluble  proteids  of  the  blood 
plasma,  destroyed  by  heating  to  55°  C.,  capable  of  de- 
stroying various  kinds  of  bacteria. 

Hemolysins  are  similar  substances  which  are  able 
to  destroy  the  red  blood-cells  of  another  species. 

The  increase  of  bacteriolysins  in  the  blood  may  be 
accomplished  by  the  injection  of  increasing  but  non- 
fatal  doses  of  bacteria  or  their  products  into  the  circu- 
lation. 

The  hemolytic  power  of  blood  may  be  developed  to 
greater  than  normal  degree  in  a  similar  manner. 

On  analysis  by  experimental  methods  it  is  found  that 
the  bacteriolysin  or  hemolysin  consists  of  two  sub- 
stances, called  the  immune  body  and  the  complement. 
The  bacteria  or  cell  destroying  substances  of  the  blood 
cannot  act  upon  their  objects  of  attack  without  an  in- 
termediary substance,  a  substance,  as  it  were,  with  two 
chemical  affinities,  the  immune  body  which  is  found  to 
be  specific  for  each  bacteriolysin  or  hemolysin  which  is 
developed,  and  when  the  action  has  taken  place  the 
immune  body  is  considered  to  be  united  to  the  bacterial 
product  on  one  side  and  the  blood  complement  upon 
the  other. 

A  further  property  of  the  blood  is  a  power  of  agglu- 
tinating or  clumping  and  rendering  immobile  the  bac- 


THE  LYMPH.  35 

teria  which  it  mav  be  called  upon  to  attack.  This 
property  also,  though  present  at  all  times,  is  capable 
of  development  and  increase,  as  is  seen  in  the  course 
of  various  diseases;  as,  for  example,  in  typhoid  fever, 
where  the  specific  agglutinins  or  the  patient's  blood 
are  so  developed  as  to  show  a  clumping  of  typhoid  bac- 
teria when  the  patient's  serum  and  a  culture  of  typhoid 
bacteria  are  brought  together. 

Coincident  with  the  increase  of  hemolytic  power  de- 
veloped by  injecting  the  blood  of  one  species  of  animal 
into  another  species,  there  are  developed  specific  pre- 
cipitins.  If  the  serum  is  taken  from  a  rabbit  which 
ha-  for  a  period  of  weeks  had  small  subcutaneous  doses 
of  human  blood  serum,  and  is  added  to  human  blood 
-tri i in,  a  precipitate  will  occur,  which  will  not  take 
place  when  such  adapted  rabbit  serum  is  added  to  the 
blood  of  any  other  animal,  except  that  of  the  anthro- 
poid apes.  This  is  the  so-called  Biological  test  for  the 
source  of  a  suspected  blood. 

THE  LYMPH. 

Lymph  is  formed  by  the  filtration  of  plasma  through 
the  walls  of  the  capillaries  into  the  lymph-spaces,  which 
lie  outside  the  capillaries  and  between  the  cells  of  the 
various  tissues.  Its  composition  is,  however,  not  pre- 
ci.-ely  the  same  as  that  of  the  plasma,  owing  to  the  fact 
that  the  proteids  do  not  pass  through  the  capillary  wall 
a-  readily  as  do  the  other  constituents  of  the  plasma. 
The  capillaries  of  different  parts  of  the  body  differ  in 
their  permeability,  those  of  the  liver  being  the  most 
permeable,  those  of  the  lower  limbs  the  least  so;  con- 
Bequently,  the  lymph  formed  in  different  parts  differs 
in  composition ;  that  formed  in  the  liver  may  contain 
protcid.-  to  the  extent  of  6^  ;  that  formed  in  the  legs, 
about 


3(3  PROTOPLASM,  BLOOD,  AND  LYMPH. 

The  force  concerned  in  causing  the  filtration  of  the 
plasma  into  the  lymph-spaces — in  other  words,  in  the 
formation  of  the  lymph — is  the  intracapillary  blood 
pressure.  To  this  force  are  opposed  the  following :  the 
slight  resistance  offered  by  the  capillary  wall  to  the 
passage  through  it  of  water  and  inorganic  salts ;  the 
much  more  effective  resistance  which  is  opposed  to  the 
passage  of  proteids ;  and  the  osmotic  pressure  which  is 
exerted  by  that  portion  of  the  proteids  which  does  not 
pass  through  the  wall,  but  remains  within  the  capil- 
laries. This  portion  is  usually  the  larger.  Proteids 
form  about  8  ^  of  the  plasma,  and  exert  an  osmotic 
pressure  of  about  30  mm.  of  mercury  ;  the  lymph  con- 
tains about  3  <f0  proteids  with  an  osmotic  pressure  of  10 
mm.  of  mercury  or  a  little  more,  exerted  in  the  opposite 
direction  ;  so  that  the  balance  of  osmotic  pressure 
which  is  effective  in  resisting  the  outward  passage  of 
lymph  amounts  to  about  20  mm.  Hg.  The  intracapil- 
lary blood  pressure  is,  under  ordinary  circumstances, 
from  30  to  50  mm.  Hg,  and  suffices  to  overcome  the 
opposing  forces  which  have  been  mentioned  above  ;  but 
if  for  any  reason — e.  g.,  after  severe  hemorrhage — the 
intracapillary  pressure  falls  below  20  mm.  Hg,  the 
effective  balance  of  osmotic  pressure,  due  to  the  pre- 
dominance of  proteids  within  the  capillaries  will  cause 
the  absorption  of  water  from  the  lymph-spaces. 

That  portion  of  the  lymphatic  system  concerned  ii 
the  absorption  of  fat  from  the  intestine,  and  the  con- 
veying of  the  lymph  and  its  contained  emulsified  and 
saponified  fats  by  the  lacteals,  the  receptaculum  chyli, 
and  the  thoracic  duct,  to  the  blood  stream,  illustrates 
best  the  various  factors  which  control  the  flow  of  lymph 
in  various  parts  of  the  body.  They  may  .be  summed 
up  as  follows : 

1st.    Intracapillary  pressure. 


QUESTIONS.  37 

'2(\.  Force  of  diffusion  depending  upon  the  inequal- 
ity in  the  chemical  composition  of  the  blood  plasma 
:md  the  liquid  outside  of  the  capillaries,  or  between 
this  liquid  and  the  contents  of  the  tissue  elements. 

.'id.    The  force  of  osmotic  pressure. 

4th.  The  valves  in  the  lymph- vessels. 

5th.  The  negative  pressure  in  the  thorax  acting  upon 
tin-  surface  of  the  thoracic  duct. 

<>th.  The  negative  pressure  in  the  great  veins  at  the 
base  of  the  neck  acting  upon  the  opening  of  the  tho- 
racic duct  at  its  venous  junction. 

7th.  The  effect  of  contraction  and  relaxation  of  the 
skeletal,  and  visceral  musculature. 


QUESTIONS  FOR  CHAPTER  I. 

What  is  the  physiological  difference  between  plants  and  ani- 
mal-'.J 

Name  the  properties  of  a  living  cell. 

What  is  the  source  of  the  potential  energy  which  is  contained 
in  food? 

In  what  respect  does  bioplasm  resemble  dynamite? 

Why  is  it  impossible  to  convert  fat  and  carbohydrate  into  pro- 
tein! ? 

Why  is  hydrolysis  accompanied  by  the  liberation  pf  heat  ? 

Why  are  native  proteids  divided  into  two  classes? 

How  may  native  proteids  be  removed  from  a  solution  which  also 
"«>i  it  a  ins  proteoses  and  peptones,  without  removing  the  two  latter? 

What  proportion  of  a  blood  clot  consists  of  fibrin  ? 

How  does  hemoglobin  differ  from  other  proteids? 

Ho\\  may  albumins  be  separated  from  globulins? 

Give  the  functions  of  the  blood  as  a  whole,  and  of  the  red  cells 
and  leukocytes  independently. 

What  are  some  of  the  changes  which  occur  in  blood  when  it  ia 
boiled? 

What  are  the  effects  of  removing  all  the  inorganic  salts  from 
blood? 


38 


PROTOPLASM,  BLOOD,  AND  LYMPH. 


Does  the  "salting"  of  blood  prevent  the  formation  of  fibrin- 
ferment,  or  does  it  prevent  its  activity  ? 

Does'the  addition  of  fibrin-ferment  to  defibrinated  blood  cause 
it  to  clot  ? 

How  may  defibrinated  blood  be  caused  to  clot  ? 

If  the  coagulation  of  blood  be  prevented  by  rapidly  cooling  it 
to  0°  C.,  and  keeping  it  at  this  temperature  until  most  of  the  cells 
have  settled,  and  if  the  upper  and  lower  layers  of  plasma  be  sep- 
arated and  warmed,  which  will  coagulate  first  ? 

By  what  different  methods  may  fibrinogen  be  removed  from  the 
blood,  without  at  the  same  time  removing  the  other  proteids? 

What  effect  has  the  addition  of  defibrinated  blood  on  a  solution 
of  pure  fibrinogen? 

What  is  the  effect  of  introducing  a  foreign  body  into  the  blood- 
vessels ? 

What  are  the  agencies  which  may  be  brought  into  activity  to 
resist  the  harmful  effect  of  foreign  substances  in  the  blood  stream  ? 

Why  does  the  dilution  of  salted  blood  cause  it  to  clot? 

Why  does  packing  a  wound  with  gauze  hasten  clotting  ? 

How  may  we  determine  whether  a  given  reaction  is  caused  by 
an  enzyme? 

Is  lymph  a  product  of  the  lymphatic  glands  ? 

What  is  the  difference  between  lymph  and  serum  ? 

What  are  the  important  constituents  of  lymph  ? 

Why  does  serum  remain  liquid  at  0°  C.  ? 

How  may  the  osmotic  pressure  of  plasma  be  reduced  ? 

Why  should  distilled  water  not  be  injected  into  the  blood-ves- 
sels? 

Why  does  an  organ  that  is  removed  from  the  body  quickly  lose 
its  irritability? 

The  osmotic  pressure  of  the. plasma  is  due  chiefly  to  the  inor- 
ganic salts  which  are  present  in  small  quantity.  Why,  then,  are 
the  proteids  of  greater  importance  in  relation  to  the  exchange  of 
water  between  the  plasma  and  lymph  ? 

Does  a  \%  solution  of  maltose  or  a  \%  solution  of  dextrose 
possess  the  higher  osmotic  pressure  ?  Why  ? 


CHAPTER  II. 
THE  CIRCULATION  OF  THE  BLOOD. 

The  Heart. — The  blood  is  inclosed  in  a  system  of 
<  la-tic  tubes,  the  blood-vessels,  a  portion  of  which  has 
1)«  n  developed  into  a  muscular  pump,  the  heart,  which 
|M»scsses  the  power  of  rhythmic  contraction  and  relaxa- 
tion. As  the  heart  relaxes,  blood  flows  into  it  from  the 
veins ;  as  it  contracts,  blood  is  forced  out  into  the  arteries. 
The  direction  in  which  the  blood  flows  through  the  heart 
is  determined  by  the  valves,  which  open  toward  the 
arteries  only.  The  heart  is  divided  into  two  halves,  the 
right  heart  and  the  left ;  shortly  after  birth  an  opening 
which  connects  the  cavities  of  the  two  hearts  closes, 
leaving  them  with  no  communication.  Each  half  pos- 
-< --eg  two  chambers,  an  auricle  and  a  ventricle;  the 
muscular  wall  of  the  ventricle  being  much  thicker,  in 
each  case,  than  that  of  the  auricle,  and  the  wall  of  the 
left  ventricle  much  thicker  than  that  of  the  fight.  This 
arrangement  corresponds  with  the  amount  of  work  done 
by  the  walls  of  the  different  chambers.  The  blood* 
pumped  out  by  the  right  ventricle  enters  the  pulmonary 
artery,  and  is  distributed  through  its  branches  to  the 
capillaries  of  the  lungs,  where  it  is  arterialized  ;  thence 
it  flows  through  the  pulmonary  veins  to  the  left  heart, 
by  which  it  is  forced  out  into  the  aorta.  The  elastic 
wall  of  the  aorta,  always  in  a  state  of  distention,  forces 
the  blood  onward  through  the  smaller  arteries,  through 
the  capillaries,  and  through  the  veins,  back  to  the  right 

39 


40  THE  CIRCULATION  OF  THE  BLOOD. 

heart.  The  distention  of  the  aorta  is  due  to  the  fact 
that  it  requires  more  force  to  quicken  the  flow  of  blood 
through  the  small  arterioles  and  capillaries  than  it  does 
to  stretch  the  aorta  and  larger  arteries.  Thus  the  elas- 
ticity of  the  aorta  and  larger  arteries  lessens  the  work 
which  is  required  of  the  heart. 

Between  the  right  auricle  and  ventricle  is  placed  the 
tricuspid  valve  ;  between  the  right  ventricle  and  pul- 
monary artery,  and  at  the  root  of  the  latter,  is  the  pul- 
monary set  of  semilunar  valves.  The  mitral  valve  is 
set  between  the  left  auricle  and  ventricle,  while  the 
aortic  set  of  semilunar  valves,  at  the  root  of  the  aorta, 
separates  this  vessel  from  the  left  ventricle. 

The  Heart  Cycle. — The  cardiac  beat  is  initiated  by  a 
contraction  of  the  muscular  libers  in  the  walls  of  the  large 
veins  close  to  the  auricles.  The  contraction  spreads  to, 
and  sweeps  over,  the  auricular  musculature,  driving  the 
contents  of  the  auricles  into  the  ventricles,  and  constitut- 
ing the  auricular  systole.  This  merely  completes  the  nil- 
ing  of  the  ventricle,  in  which,  previous  to  the  systole  of 
the  auricle,  blood  has  accumulated  by  inflow,  through 
the  latter,  from  the  veins.  The  auricular  systole  lasts 
but  0.1  of  a  second,  and  is  followed  by  the  systole  of 
the  ventricles.  Were  it  not  for  the  auricles,  the  flow 
of  blood  from  the  veins  into  the  heart  would  be  checked 
during  the  ventricular  systole ;  as  it  is,  the  auricles  not 
only  assist  in  the  filling  of  the  ventricles,  but  constitute 
a  time-saving  reservoir  which  is  of  special  value  when 
the  heart  rhythm  is  rapid. 

As  the  ventricles  fill,  the  free  edges  of  the  auriculo- 
ventricular  valves  are  carried  upward  and  approach 
one  another,  their  complete  closure  being  effected  by 
the  rise  of  pressure  within  the  ventricles,  at  the  begin- 
ning of  ventricular  systole.  The  intraventricular 
pressure  rises  rapidly  as  the  systole  proceeds,  the  back- 


THE  HEART.  41 

flow  of  blood  into  the  auricles  being  prevented  by  the 
tricuspid  and  mitral  valves,  which  are  held  in  place  by 
their  tendinous  cords ;  while  the  outflow  into  the 
arteries  is,  for  the  moment,  prevented  by  the  semilnnar 
valves,  which  are  kept  closed  by  the  higher  pressures 
in  the  pulmonary  artery  and  aorta.  As  soon,  however, 
as  the  pressure  within  the  ventricle  rises,  in  the  one 
case,  higher  than  that  in  the  pulmonary  artery,  in  the 
other,  above  that  in  the  aorta,  the  semilunar  valves 
must  open  .as  the  blood  is  ejected  by  the  ventricles  into 
the  arteries.  The  ventricles  probably  never  completely 
empty  themselves,  and  they  are  far  from  doing  so  when 
the  heart  is  beating  slowly.  Then  follows  the  ventri- 
cular diastole,  or  period  of  relaxation  and  rest,  at  the 
'gi nning  of  which  the  pressure  within  the  ventricle 
falls  below  that  in  the  aorta,  the  semilunar  valves 
being  closed  in  consequence.  A  short  interval  elapses 
before  the  intraventricular  pressure  falls  below  that 
within  the  auricle,  and  until  this  point  is  reached  the 
auriculo- ventricular  valves  must,  of  course,  remain 
closed.  The  whole  series  of  events  just  described 
occurs  simultaneously  in  the  right  and  left  hearts,  and 
constitutes  a  heart  cycle.  When  the  heart  beats  with 
average  frequency, — that  is,  seventy-two  times  a  min- 
ute,—each  cycle  lasts  about  0.8  of  a  second,  and  may 
be  tabulated  as  in  Table  2  (p.  42). 

It  will  be  noticed  that  while  the  auricular  systole 
lasts  0.1  of  a  second,  and  the  diastole  0.7,  the  systole 
of  the  ventricle  occupies  0.3,  and  its  diastole  0.5  of  a 
second,  the  ventricular  cycle  beginning  0.1  of  a  second 
later  than  that  of  the  auricle,  and  lasting  to  the  end  of 
the  first  tenth  of  a  second  in  the  succeeding  auricular 
cycle.  When  the  frequency  of  the  heart-beat  is  in- 
creased, each  cycle  is,  of  course,  shortened,  this  reduc- 
tion being:  accomplished,  for  the  most  part,  at  the 


42 


THE  CIRCULATION  OF  THE  BLOOD. 


4- 


4- 


t . 


t   t 


rf         t 


4.4. 


a,   ®  -0   C   ^  0 


THE  HEART.  43 

< 'Xpcnse  of  the  diastole,  the  systole  of  the  ventricle 
lasting  almost  as  long  :ls  usual. 

The  behavior  of  the  valves  depends  upon  the  rela- 
tive height  of  the  pressure  on  either  side  of  them  ;  the 
auriculo-ventricular  valves,  for  instance,  remain  closed 
as  long  as  tin-  pressure  within  the  ventricle  is  higher 
than  that  in  the  auricle;  when  the  pressure  within  the 
auricle  rises  above  that  in  the  ventricle,  they  open,  and 
remain  so  until  the  intraventricular  pressure  again 
predominates.  In  the  same  way,  the  semilunar  valves 
are  kept  closed  by  an  arterial  pressure  that  is  greater 
than  the  intraventricular  pressure,  and  give  way  when 
the  ventricular  rises  above  the  arterial.  It  will  be 
noticed  that  both  sets  of  valves  are,  for  two  short 
pi-rinds,  closed  at  the  same  time. 

The  rate  at  which  the  heart  beats  is  governed  by  the 
<•<  ntral  nervous  system,  which,  in  this  respect,  exerts 
it-  emu  rol  chiefly  over  the  auricles,  the  auricular  rhythm 
s<  1 1  i iiii  t he  pace  for  the  ventricles.  The  auricular  stimu- 
lu-  is  probably  transmitted,  not  by  nerve-fibers,  but  by 
the  contraction  of  a  few  muscle-fibers  connecting  the 
auricles  with  the  ventricles.  If  the  auricles  are  caused 
t<>  -top  beating  by  the  stimulation  of  the  pneumogastric 
urrve,  the  ventricles,  after  a  brief  pause,  begin  to  beat 
with  a  much  slower  rhythm  of  their  own. 

Although  the  central  nervous  system  controls  the 
heart-beat,  it  is  by  no  means  essential  to  its  continuance, 
a-  may  be  shown  by  removing  the  heart  from  the  body, 
when,  if  properly  supplied  with  oxygenated  blood,  it 
may  go  on  beating  for  hours.  The  cardiac  muscle 
itself  seems  to  possess  an  inherent  power  of  rhythmic 
contraction,  for  even  small  isolated  pieces  of  the  ven- 
tricle which  appear  to  contain  no  nerve-cells  will  beat 
rhythmically  if  supplied  with  arterial  blood* 

Heart  Sounds. — If  the  ear  be  placed  against  the 


44  THE  CIRCULATION  OF  THE  BLOOD. 

chest-wall,  two  sounds  are  heard  each  time  the  heart 
beats.  The  first  accompanies  the  ventricular  systole,  and 
is  more  prolonged  than  the  second,  which  is  diastolic  (see 
Table  2).  The  first  sound,  which  seems  to  be  compound, 
is  probably  produced  in  part  by  the  contraction  of  the 
ventricle,  and  in  part  by  the  vibration  of  the  auriculo- 
ventricular  valves  on  closure.  Each  ventricle  takes  part 
in  the  production  of  the  first  sound.  Disease  of 
either  of  the  auriculo-ventricular  valves  produces  a 
change  in  the  valvular  element  of  the  sound,  which,  in 
the  case  of  mitral  abnormality,  is  best  appreciated  by 
placing  the  ear,  or  stethoscope,  over  the  fifth  left  inter- 
costal space,  at  the  point  where  the  apex-beat  of  the  left 
ventricle  may  be  seen  or  felt ;  evidence  of  tricuspid 
error  being  best  heard  just  to  the  right  of  the  sternum, 
at  about  the  same  level. 

The  second  sound  occurs  at  the  beginning  of  the  ven- 
tricular diastole,  and  is  due  to  the  vibration  of  the 
semilunar  valves  at,  or  just  after,  their  closure.  Th 
aortic  sound  is  most  clearly  heard  at  the  point  where 
the  second  right  costal  cartilage  joins  the  sternum  ; 
while  the  closure  of  the  pulmonary  semilunar  valve  is 
most  distinct  over  the  second  left  intercostal  space,  close 
to  the  sternum.  It  is,  however,  impossible  to  distin- 
guish between  the  normal  aortic  and  pulmonary  sounds, 
though  an  abnormality  in  one  set  may  be  located  in  tin 
way. 

If  the  rate  at  which  the  blood  flows  through  vessel 
of  different  size  be  compared,  it  will  be  seen  that  th 
larger  the  vessel,  the  greater  the  speed.     In  the  ao 
the  blood  flows  most  rapidly,  for  the  sectional  area  o 
this  vessel  is  smaller  than  the  united  sectional  area  of 
its  branches,  consequently  the  blood,  having  less  room, 
must  flow  more  quickly.     The  rate  of  flow  is  inversely 
proportional  to  the  width  of  bed.     The  united  sectional 


THE  HEART.  45 

area  of  the  systemic  capillaries  has  been  estimated  to  be 
a>  iiiiidi  as  SOU  times  that  of  the  aorta;  in  this  dis- 
trict, then,  the  stream  is  sluggish.  As  the  blood  flows 
from  the  capillaries  into  the  small  veins,  the  width  of 
bed  decrease's,  and  the  stream  quickens;  in  large  veins 
the  rate  will  approach,  but  never  equal,  that  in  the 
aorta.  The  velocity  of  the  circulation,  as  a  whole,  of 
co ii r>«-  iiim-ases  or  decreases  with  a  change  in  the  rate 
and  strength  of  the  heart-beat.  .. 

Blood  Pressure. — The  blood  as  it  flows  through  the 
ve-sels  is  under  constant  pressure.  This  pressure  is  the 
product  of  the  propelling  force  exerted  by  the  heart,  and 
the  resistance  offered  to  the  flow  by  hydraulic  friction. 
During  the  diastole  of  the  ventricle,  the  flow  is  kept  up 
\>\-  the  elastic  and  overfilled  aorta  and  larger  arteries. 
As  li(|iiid  flows  through,  a  tube,  friction  exists  between 
it-  particles;  and  the  nearer  the  wall  of  the  tube,  the 
greater  the  friction  ;  therefore,  if  we  compare  the  flow 
of  liquid  through  a  large  tube  with  its  flow  through  a 
number  of  small  tubes,  the  united  sectional  area  of 
which  is  equal  to  the  sectional  area  of  the  large  tube, 
we  shall  find  that  it  meets  with  much  more  resistance 
iu  the  small  ones;  for  a  much  larger  proportion  of  the 
liquid  will  flow  in  the  neighborhood  of  the  tube-wall, 
and  the  friction  will  be  greater.  The  blood,  then,  will 
meet  with  most  resistance  on  passing  through  the  innu- 
merable arterioles  and  capillaries,  into  which  the  larger 
arteries  divide;  this  is  usually  spoken  of  as  the  per- 
ipheral resistance.  The  overcoming  of  this  periph- 
eral resistance  uses  up  most  of  the  heart  force,  and,  by 
the  time  the  blood  reaches  the  veins,  it  flows  under  but 
little  pressure,  which,  however,  suffices  to  carry  it  as  far 
as  the  right  heart.  The  fall  in  pressure  js-continuous 
from  the  beginning  of  the  aorta  to^the  ending  of  the 
veins,  for  friction  comes  into  play  along  the  whole  route, 


46  THE  CIRCULATION  OF  THE  BLOOD. 

though  in  the  larger  vessels  it  is  but  slight.  In  the 
arteries  the  fall  is  a  gradual  one,  but  it  becomes  abrupt 
in  the  arteriole  and  capillary  district,  while  in  the  veins 
the  pressure  again  decreases  slowly. 

The  blood  pressure  is  variable,  especially  that  in  the 
arteries.  As  there  are  two  factors  in  the  production  of 
the  blood  pressure,  so  there  are  two  main  causes  con- 
cerned in  bringing  about  its  variation  ;  namely,  (a)  a 
change  in  the  propelling  force,  the  heart-beat,  and  (b) 
a  change  in  the  peripheral  resistance.  A  third  cause 
consists  in  an  alteration  of  the  capacity  of  the  vessels, 
more  especially  of  the  large  veins.  An  increase  in  the 
rate  and  strength  of  the  heart-beat  naturally  raises  the 
pressure  in  the  arteries  and  capillaries,  and  since  the 
heart  transfers  blood  from  the  veins  into  the  arteries, 
the  pressure  in  the  large  veins  must  under  these  cir- 
cumstances be  lowered.  When  the  activity  of  the  heart 
is  depressed,  the  resulting  changes  in  blood  pressure  are 
the  opposite  of  those  just  enumerated.  While  elastic 
tissue  is  a  characteristic  feature  in  the  walls  of  the  large 
arteries,  in  the  arterioles  muscular  tissue  predominates, 
and  gives  to  these  small  vessels  the  important  property 
of  varying  their  caliber.  With  a  change  in  their  size, 
the  resistance  which  they  offer  to  the  blood  flow  also 
varies ;  a  wide-spread  constriction  of  the  arterioles  re- 
sulting in  a  marked  rise  in  arterial  pressure,  Avhile  a 
great  fall  accompanies  their  general  relaxation,  for  the 
blood,  under  these  circumstances,  flows  more  readily 
from  the  arteries  into  the  capillaries.  The  highest 
possible  arterial  pressure  is  attained  by  a  general  con- 
striction of  the  arterioles,  accompanied  by  a  strong  and 
rapid  heart-beat.  A  very  low  pressure  will  result  from 
a  general  dilatation  of  the  arterioles  and  a  slow,  weak 
heart-beat ;  if  at  the  same  time  the  walls  of  the  large 
veins  and  of  the  branches  of  the  portal  vein  relax,  the 


NERVOUS  CONTROL.  47 

hloud  will  tend  t<>  stagnate  in  these  veins,  and,  since 
little  blond  will  reach  the  heart,  but  little  can  be 
pumped  into  the  arteries,  in  which  the  pressure  will 
tall  to  a  dangerous  extent. 

Nervous  Control. — The  heart  is  controlled  by  the 
central  nervous  system,  through  two  sets  of  nerves  ;  one 
Bet,  arising  from  the  Cardio-inhibitory  Center,  lessens  its 
activity  ;  the  other,  carrying  impulses  from  the  Accelera- 
tor or  Augmentor  Center,  quickens  and  strengthens  the 
beat.  The  eardio-inhibitory  nerve-fibers  reach  the  heart 
through  the  pneumogastric,  and  probably  exert  their  in- 
fluence  over  the  heart  muscle,  not  directly,  but  through 
the  mediation  of  nerve-cells  which  are  situated  in  the 
wall  of  the  organ.  On  division  of  both  pneumogastric 
nerves,  in  the  neck,  the  heart  beats  more  rapidly,  for 
the  controlling  influence  of  the  center  is  thus  cut  off. 
If  the  end  of  the  peripheral  .portion  of  one  of  these 
divided  nerves  be  stimulated  with  electric  shocks,  the 
heart-beat  will  become  slow,  or,  if  the  current  be  strong, 
will  stop  for  a  short,  time.  The  auricles  may,  in  this 
way,  l>e  prevented  from  beating  for  an  hour  or  more  if 
the  stimulation  be  kept  up;  but  the  ventricles,  after  a 
short  pause,  begin  to  beat  at  a  slower  rate  than  before. 
The  diastole  is  very  much  prolonged,  and,  of  course, 
uives  time  for  the  accumulation  within  the  heart  of 
more  blood  than  usual  between  beats  ;  the  ventricle  thus 
dilated  fails  to  empty  itself  ;  indeed,  to  such  an  extent 
i.>  thi-  the  case  that  a  slowly  beating  heart  may,  at  the 
end  of  its  systole,  contain  more  blood  than  it  usually 
contains  at  the  beginning  of  the  contraction.  This 
residual  blood  will,  in  the  succeeding  diastole,  retard 
the  inflow  from  the  veins,  and,  in  consequence,  less 
blood  will  enter  the  heart  in  a  given  time,  and  the  pres- 
sure in  the  large  veins  will  rise.  Since  less  blood  enters 
the  heart  in  a  given  time,  less  will  be  pumped  out  into 


48  THE  CIRCULATION  OF  THE  BLOOD. 

the  arteries,  and  the  arterial  pressure  falls.  Although 
the  output  of  the  ventricle  is  decreased,  the  contraction 
volume — that  is,  the  amount  forced  out  by  a  single  con- 
traction— is  increased.  To  repeat,  then,  a  slow  heart- 
beat results  in  a  dilatation  of  the  ventricle  and  a  rise 
of  venous  pressure,  a  lessened  output,  and  a  fall  of 
arterial  pressure. 

The  cardio=inhibitory  center  is  situated  in  the  spinal 
bulb,  and  is  bilateral.  It  is  continually  active,  and  this 
tone  may  be  increased  or  decreased  in  a  variety  of 
ways  ;  for  instance,  a  rise  of  arterial  pressure  increases 
its  activity,  the  importance  of  this  fact  being  apparent, 
for  any  abnormal  rise  of  pressure  will  tend  to  bring 
about  its  own  fall  by  lessening  the  output  of  the  heart, 
through  stimulation  of  this  center.  The  center  is  not 
only  affected  by  the  pressure  at  which  the  blood  flows 
through  the  neighboring  vessels,  but  it  is  also  sensitive 
to  its  chemical  composition ;  if  the  blood  becomes 
unusually  venous,  the  center  is  stimulated.  A  reflex 
slowing  of  the  heart  may  be  caused  by  the  stimulation 
of  various  sensory  nerves ;  for  instance,  the  nasal 
branch  of  the  trifacial,  as  on  the  inhalation  of  chlo 
form  or  ammonia  vapor  into  the  nostrils.  A  reflex 
event  is  one  which  is  produced  by  the  passage  of 
an  afferent  nerve-impulse  from  the  periphery  to  a 
center,  the  center  responding  by  the  dispatch  of  an 
efferent  (outward)  impulse  which  brings  about  the  even 
be  it  the  contraction  of  a  muscle,  secretion  by  a  gland 
or  inhibition  of  the  heart.  A  reflex  slowing  of  th 
heart  is  readily  caused  by  stimulating  the  afferem 
nerve-fibers  of  the  pneuniogastric  ;  these  fibers  normally 
carry  afferent  impulses  from  the  lungs,  heart,  liver, 
stomach,  etc.,  to  the  spinal  bulb,  but  not  all  of  them 
necessarily  reach  the  cardio-inhibitory  center.  During 
expiration  the  heart  beats  slowly,  owing  to  afferent 


NERVOUS  CONTROL.  49 

impulses  from  the  lungs,  which,  on  reaching  the  bulb, 
alVect  the  center  either  directly  or  through  the  interven- 
tion <»!'  the  respiratory  center.  It  may  also  be  inhibited 
bv  aH'cn-nt  nerve  impulses,  as,  for  instance,  through 
the  glossopharyngeal  nerve  during  swallowing;  this 
may,  however,  he  another  case  of  irradiation  from  the 
respiratory  center.  An  inhibition  of  the  cardio-inhib- 
itory  center  of  course  allows  the  heart  to  beat  more  rap- 
idlv.  The  quickening  of  the  heart-beat  which  follows 
the  administration  of  atropin  depends  upon  a  partial  or 
complete  paralysis  of  the  endings  of  the  inhibitory 
lihers  in  the  heart.  The  center  is  also  under  the  influ- 
ence <>f  the  emotions. 

The  cardio=augmentor  center  is  probably  also  situ- 
ated in  the  spinal  bulb;  the  nerve-fibers  arising  from 
it  descend  the  spinal  cord  as  far  as  the  upper  end  of 
the  thoracic  region,  where  they  probably  end,  but  make 
physiologic  connection  in  the  gray  matter  with  nerve- 
cells  whose  fibers  pass  out  through  the  upper  thoracic 
ventral  nerve-roots;  in  the  dog,  through  the  second 
and  third.  They  join  the  sympathetic  chain,  and 
probably  end  in  the  ganglion  stellaturn,  where  a  second 
cell  station  intervenes,  the  fibers  originating  from  the 
ganglion  cells  passing  to  the  heart  muscles.  This  last 
of  nerve-libers  come  under  the  head  ot  what  are 
known  a-  post-ganglionic  fibers  of  the  sympathetic 
-\M<m,  in  contradistinction  to  the  fibers  of  the  second 
>et  mentioned,  the  pre-ganglionic  sympathetic  fibers, 
which,  originating  from  cells  situated  in  the  gray  matter 
of  the  >|»inal  cord,  end  in  sympathetic  ganglia.  The 
nervous  chain  which  connects  the  spinal  cord  with  in- 
voluntary tissue,  such  as  plain  muscle,  cardiac  muscle, 
and  glandular  epithelium,  usually,  if  not  always,  con- 
sists of  two  links — pre-gangl ionic  and  post-ganglionic 
nerve-fibers.  If  the  augmentor  center  possesses  tone, 


50  THE  CIRCULATION  OF  THE  BLOOD. 

— that  is,  is  continuously  active, — as  seems  probable, 
its  influence  over  the  heart-beat  is  not  so  marked  as 
that  of  the  inhibitory  center.  The  stimulation  of  the 
augmentor  nerves  increases  the  strength  of  both  the 
auricular  and  the  ventricular  contraction,  the  output  of 
the  venticle  is  increased,  the  venous  pressure  is  lowered, 
and  the  arterial  pressure  raised.  During  muscular 
exercise  the  augmentor  center  is  stimulated  by  the 
chemical  waste  products  of  muscular  metabolism,  which 
proceeds  more  rapidly  during  activity  than  during 
rest.  A  rise  of  body- temperature  also  directly  stimu- 
lates the  center.  A  reflex  quickening  of  the  heart 
may  be  provoked  by  the  stimulation  of  almost  any 
nerve-trunk,  but  is  usually  followed  by  slowing,  owing 
to  the  simultaneous  or  subsequent  stimulation  of  the 
inhibitory  center  through  the  same  channel.  As  is 
well  known,  the  heart-beat  may  be  quickened  by  the 
emotions. 

Nervous  control  is  not  the  only  cause  of  variation 
in  the  strength  of  the  heart-beat;  the  quantity  and 
quality  of  the  coronary  blood  supply  also  exert  an  in- 
fluence. The  effect  of  an  alteration  in  the  amount  of 
blood  supplied  to  the  heart  is  much  more  marked  in 
regard  to  strength  than  frequency.  The  ventricle  beats 
more  strongly  when  its  coronary  blood  supply  is  in- 
creased. A  high  arterial  blood  pressure  is  favorable 
to  a  strong  heart-beat,  unless  the  ventricle  becomes 
dilated  in  consequence,  in  which  case  the  coronary  cir- 
culation is  retarded.  A  moderately  high  pressure  also 
increases  the  force  of  the  heart-beat,  owing  to  the  fact 
that  muscles  work  to  better  advantage  against  a  certain 
amount  of  resistance.  The  quality  of  the  blood  is  im- 
portant, especially  in  regard  to  the  amount  of  oxygen 
contained. 

The  variation  of  the  peripheral  resistance  is  also 


NERVOUS  CONTROL.  51 

under  the  control  of  the  central  nervous  system.  There 
exi-ts  in  the  spinal  bull)  a  center,  known  as  the  vaso- 
constrictor center,  which  exerts  an  influence  over  the 
muscular  walls  of  the  vessels,  most  evident  in  the  ca.-e 
of  the  arterioles.  As  in  the  case  of  the  cardie-inhibi- 
tory center,  the  activity  of  this  center  is  continuous, 
and  its  tone  is  variable.  Like  the  inhibitory  center, 
it  acts  as  a  regulatory  mechanism  whereby  the 
blond  pressure  is  kept  fairly  constant.  If  the  arte- 
rial pressure  falls,  this  center  becomes  more  active,  and 
brings  about  a  constriction  of  the  arterioles,  thus  rais- 
ing the  peripheral  resistance,  and  with  it  the  arterial 
blood  pressure.  It  is  also  stimulated  by  a  venous  con- 
dition of  the  blood,  the  arterial  pressure  rising  to  a 

•  •Teat    height  during  dyspnea,  in  spite  of  the  simulta- 
neous inhibition  of  the  heart.     Its  activity  is  reduced 
by  certain   drugs,  such  as   chloroform,  ether,  alcohol, 
etc.     It  may  be  indirectly  stimulated  through  almost 
any  afferent  nerve;  for  instance,  the  application  of  cold 
to  the  skin,  by  stimulating  the  cutaneous  nerves,  and 
thus  indirectly  influencing  the  constrictor  center,  brings 
about  a  reflex  paling  of  the  skin.     On  the  other  hand, 
the  application  of  warmth  causes  a  reflex  dilatation  of 
the    cutaneous    vessels,    by   inhibiting    the    constrictor 

•  •••liter.     One  afferent  nerve  which  transmits  impulses 
fmiu  the  heart  to  the  spinal  bulb,  and  is  known  as  the 
depressor  nerve,  is  of  special  importance  through  its 
relation  to  this  center,  and  consequent  influence  on  the 
IVM  illation  of  the  blood  pressure.     When  the  arterial 
piv— ure    rise,s   unduly,  the  intracardiac  pressure   inu.-t 

ri.-c,  and  in  so  doing  stimulates  the  endings  of  the 
,r  nerve;  this  results  in  the  passage  through 
the  nerve  of  impulses  which,  on  reaching  the  bulb, 
inhibit  the  constrictor  center.  The  activity  of  the 
center  being  reduced,  the  arterioles  are  allowed  to 


52  THE  CIRCULATION  OF  THE  BLOOD. 

dilate,  the  peripheral  resistance  is  lessened,  and  the 
arterial  pressure  falls.  The  depressor  nerve  thus 
serves  as  a  safeguard  against  any  undue  rise  of  arterial 
pressure,  and  affords  the  heart  protection  against  over- 
work. As  in  the  case  of  the  centers  which  regulate 
the  heart-beat,  this  center  also  may  be  influenced  by 
the  emotions ;  for  example,  blushing  is  due  to  its  inhi- 
bition by  nerve  impulses  descending  from  the  brain. 

The  control  exercised  over  the  vessels  by  the  con- 
strictor center  is  specialized,  for  although  it  maintains 
a  general  vascular  tone,  it  does  not,  as  a  rule,  cause 
marked  contraction  of  all  the  arterioles  at  the  same 
time  ;  if  the  vessels  of  the  skin  be  unusually  constricted, 
those  of  the  viscera  are  allowed  to  dilate,  and  vice 
versa.  This  arrangement  insures  a  more  even  blood 
pressure  than  would  otherwise  exist. 

The  course  of  the  constrictor  nerve=fibers  resem- 
bles, to  a  certain  extent,  that  followed  by  the  cardio- 
augmentors.  The  nerve-fibers  originating  in  the  center 
pass  down  the  spinal  cord,  to  end  in  the  gray  matter 
at  different  levels  of  the  thoracic  and  upper  lumbar 
regions.  The  ends  of  the  fibers  make  physiologic  con- 
nection with  nerve-cells  whose  axons,  usually  of  small 
caliber,  pass  out  through  the  anterior  spinal  nerve-roots 
to  enter  the  sympathetic  system  as  pre-ganglionic  fibers. 
They  end  in  one  or  other  of  the  sympathetic  ganglia  in 
contact  relations  with  cells  whose  axons,  post-ganglionic 
fibers,  usually  nonmedullated,  are  distributed  to  the 
arterioles  in  almost  every  part  of  the  body.  The  post- 
ganglionic  fibers  which  innervate  the  vessels  of  the 
skin  reach  their  destination  by  passing  through  a  gra 
ramus  communicans  to  the  spinal  nerve  supplying  the 
cutaneous  area  in  question  (Fig.  4.)  ;  those  for  the 
visceral  arterioles  do  not  reenter  a  spinal  nerve,  but 
reach  the  viscera  through  the  sympathetic  (Fig.  5) 


^*JK-V 


twAf  V 


Fig.  4. 


Q/rVvt-vx^  b    -rCp 

>KcU.    U 

-/•••"' 


Fig.  5. 


NKIIVOUS  CONTROL.  55 

The  pre-ganglionic  fibers  for  the  head  pass  up  the 
cervical  sympathetic  and  end  in  the  superior  cervical 
sympathetic  ganglion  (Fig.  4). 

Since  all  the  vasoconstrictor  fibers  originating  from 
the  center  pass  down  the  spinal  cord  to  the  thoracic 
region,  division  of  the  cord  in  the  cervical  region  must 
he  followed  by  a  great  fall  of  blood  pressure,  for  all 
the  vessels  in  the  body  dilate;  if,  however,  the  animal 
be  kept  alive,  the  vascular  tone  will,  after  a  time, 
gradually  reappear,  depending  apparently  on  an 
increased  irritability  of  the  spinal  cord,  the  cells  from 
which  the  pre-ganglionic  fibers  originate  acting  as 
vicarious  constrictor  centers.  If,  now,  the  thoracic 
cord  is  destroyed,  the  vascular  tone  again  disappears 
for  a  time,  but  is  partly  reestablished  either  through 
the  influence  of  the  sympathetic  ganglion  cells  from 
which  the  post-ganglionic  fibers  spring,  or  owing  to  the 
independent  contraction  of  the  muscular  wall  of  the 
vessels. 

Some  veins  have  been  shown  to  possess  a  supply  of 
vasoconstrictor  nerves;  for  example,  the  portal  veins. 
Since  the  administration  of  chloroform  or  ether  tends 
to  paralyze  the  vasomotor  center,  it  is  very  important 
that  an  anesthetized  patient  be  kept  in  a  horizontal  po- 
Hiion,  lor,  otherwise,  the  blood  will  accumulate  in  the 
relaxed  abdominal  veins,  and  will,  by  force  of  gravity, 
be  prevented  from  reaching  the  heart. 

Scattered  through  the  different  regions  of  the  spinal 
cord  and  bulb  are  vasodilator  nerve-centers,  whose 
cells  o-ive  olT'axons  which,  for  the  most  part,  follow  the 
same  course  as  the  pre-ganglionic  vasoconstrictors;  no 
chief  vasodilator  center  has  been  proved  to  exist  in  the 
bulb.  The  existence  of  vasodilator  fibers  in  a  mixed 
nerve-trunk  may  be  demonM rated  by  special  methods 
of  stimulation  ;  there  are,  however,  some  nerves  which 


56  THE  CIRCULATION  OF  THE  BLOOD. 

contain  vasodilators  unmixed  with  vasoconstrictors. 
The  chorda  tympani  nerve  is  one  of  these,*  and  trans- 
mits to  the  sublingual  and  submaxillary  glands  vaso- 
dilator fibers  which  leave  the  bulb  in  the  seventh  cranial 
nerve.  On  stimulation  of  this  nerve,  the  arterioles  in 
the  glands  dilate,  and  the  blood  flows  through  them 
more  rapidly  than  before.  The  pre-gangl ionic  fibers 
of  the  chorda  tympani  end  in  contact  with  submaxillary 
and  sublingual  ganglion  cells,  from  which  post-gangli- 
onic  fibers  are  distributed  to  the  arterioles.  The  post- 
ganglionic  vasoconstrictor  fibers  for  the  arterioles  of 
these  glands  come  from  the  superior  cervical  sympa- 
thetic ganglion  by  way  of  the  carotid  plexus. 

During  the  activity  of  an  organ  its  blood  supply  is 
increased,  the  maximum  supply  being  afforded  by  the 
dilatation  of  its  own  arterioles,  the  constriction  of  the 
arterioles  in  other  parts  of  the  body,  and  a  strong  and 
rapid  heart-beat. 

The  Pulse. — If  the  blood  flow  through  an  artery  be 
compared  with  that  through  a  vein,  a  marked  difference 
will  be  observed ;  the  flow  through  the  artery  is  remittent, 
that  through  the  vein  is  constant ;  the  artery  pulsates,  the 
vein  does  not.  The  arterial  pulse  consists  in  a  rhythmic 
enlargement  and  subsequent  shrinkage  of  the  vessel 
due  to  slight  variations  in  arterial  blood  pressure.  The 
enlargement  is  caused  by  the  sudden  rise  of  pressure 
which  follows  the  ventricular  systole.  As  the  ventricle 
forces  out  its  contents  the  aortic  pressure  is  raised ;  this 
rise  is  rapidly  transmitted  throughout  the  arterial 
system,  the  vessel-wall  of  each  succeeding  portion 
expanding  as  it  is  reached  by  the  wave  of  heightened 
pressure.  The  slight  delay  in  the  transmission  of  the 
pulse  to  the  more  distant  arteries  may  be  readily 
appreciated  by  simultaneously  feeling  the  carotid,  and 
the  radial  pulse.  Were  the  arteries  rigid  tubes,  the 


THE  PULSE.  57 

transmission  of  the  pulse  would  be  instantaneous  ;  and, 
as  it  is,  the  higher  the  pressure  already  existing  in  the 
arteries,  the  more  rapidly  the  pulse  travels;  for  when 
the  pressure  is  high,  the  vessel-wall,  already  tightly 
stretched,  is  less  capable  of  further  expansion  than 
when  the  pressure  is  low.  When  the  pressure  is  high, 
the  pulse  will,  for  the  same  reason,  be  small.  A  large 
pulse  occurs  when  the  heart-beat  is  strong  and  the 
pressure ,  owing  to  peripheral  dilatation  of  the  arte- 
rioles,  is  comparatively  low.  The  small  pulse  of  high 
pressure  is  hard,  or  incompressible ;  that  is,  it  will  be 
more-  difficult  to  flatten  the  artery  with  the  finger  than 
when  the  pressure  is  low,  a  low  pressure  pulse  being 
s.ii't  and  compressible.  A  small,  hard  pulse  indicates 
high  blood  pressure;  a  large,  soft  pulse  indicates  low 
pressure  and  strong  heart-beat;  a  small,  soft  pulse 
indicates  a  weak  heart-beat  and  low  pressure. 

The  blood  flows  through  the  capillaries  and  veins  in 
a  e.  >nstant  stream,  the  pulse  having  been  extinguished 
by  the  resistance  offered  by  the  arterioles.  As  before 
-i  a  ted,  it  requires  less  force  to  stretch  the  elastic  arteries 
than  to  quicken  the  flow  past  the  peripheral  resistance, 
consequently  each  time  the  ventricle  contracts,  the 
quantity  of  blood  ejected  is  for  the  moment  -'accommo- 
dated in  the  arteries.  The  heart-force  thus  transmitted 
to  and  stored  in  the  arterial  wall  is  during  diastole 
a^ain  transferred  to  the  blood  stream,  the  arteries  being 
allowed  the  period  of  a  whole  heart  cycle  for  emptying 
into  the  capillaries  the  quantity  of  blood  which  they 
receive  during  one  systole.  In  case  the  arterioles  of  a 
limited  area  be  dilated,  the  general  arterial  pressure 
remaining  high,  a  pulse  will  appear  in  the  small  veins 
of  this  area,  and  the  blood  entering  the  veins  will  be 
arterial  in  color,  for,  owing  to  the  quickening  of  the 
Mono!  stream,  a  smaller  proportion  of  the  oxy hemo- 
globin will  be  reduced. 


58  THE  CIRCULATION  OF  THE  BLOOD. 

If  tlie  form  of  the  pulse=wa ve  be  recorded,  it  is  found 
to  consist  in  the  sudden  rapid  expansion  of  the  vessel, 
or  sudden  rise  of  pressure  within  the  vessel,  followed 
by  a  more  gradual  decrease  in  size  or  fall  of  pressure, 
the  fall  being  slightly  irregular  owing  to  the  occurrence 
of  minor  pressure  waves.  These  latter  are  more 
prominent  when  the  arterial  tension  is  comparatively  low 
and  the  heart-beat  strong.  The  most  marked  of  these 
secondary  waves  is  known  as  the  dicrotic  wave ;  it 
originates  in  the  aorta  immediately  after  the  closure  of 
the  aortic  valve,  and  is  transmitted  through  the  arteries 
in  the  wake  of  the  main  pulse-wave.  It  is  probably 
caused  by  the  closure  of  the  valves. 

The  arterial  blood  pressure  rises  and  falls  slightly  as 
a  result  of  respiration.  The  reason  for  this  is  that 
enlargement  of  the  thorax  tends,  not  only  to  cause  the 
inspiration  of  air,  but  also  to  aspirate  blood  into  the 
intrathoracic  veins  and  heart ;  while  on  collapse  of  the 
chest  during  expiration,  the  entrance  of  blood  is  less 
favored,  and  during  forcible  expiration  is  retarded. 
Consequently,  the  right  heart  receives  and  pumps 
during  inspiration  more,  and  during  expiration  less, 
blood  into  the  pulmonary  vessels.  At  the  beginning 
of  inspiration  there  is  a  slight  delay  in  the  reception  by 
the  left  heart  of  the  surplus  blood,  for  the  lungs  on 
inflation  accommodate  more  blood  than  before,  and 
thus  even  reduce  the  amount  reaching  the  left  heart. 
On  the  other  hand,  just  at  the  beginning  of  expiration 
the  supply  of  blood  to  the  left  heart  is  still  further 
increased,  for  the  excess  of  blood  contained  by  the 
inflated  lungs,  on  their  collapse,  passes  to  the  left  heart. 
The  effect,  then,  of  the  respiratory  movements  of  the 
thorax  is  that  the  left  heart  also,  after  a  slight  delay, 
receives  and  pumps  more  blood  during  inspiration,  and 
thus  raises  the  arterial  pressure ;  while,  during  expira- 


THE  PULSE.  59 

tion,  alter  a  momentarily  increased  supply,  it  receives 
and  pumps  less  blood,  and  the  arterial  pressure  falls. 

Venous  Circulation. — The  blood  in  the  veins  flows 
under  very  low  pressure,  for  most  of  the  heart-force  has 
been  used  up  in  carrying  it  past  the  peripheral  resist- 
ance. Its  flow,  however,  receives  material  assistance 
through  the  contraction  of  the  skeletal  and  visceral 
musculature,  and  through  the  aspiration  of  the  thorax. 
When  a  muscle  contracts,  it  compresses  the  veins  in  its 
neighborhood,  and,  since  they  are  provided  with  valves, 
helps  to  press  the  blood  onward  toward  the  heart. 
Forcible  expiration  of  course  retards  the  passage  of 
blood  into  the  thorax. 

The  pressure  in  the  distal  veins  does  not  fluctuate ; 
is  highest  at  the  capillaries,  and  decreases  as  the  heart 
is  approached.  At  the  upper  border  of  the  thorax  the 
Lrreat  veins  in  the  neck  show  a  variation  in  pressure 
due  to  the  greater  ease  of  emptying  during  inspiratory 
increase  of  thoracic  negative  pressure.  On  expiration 
the  veins  are  seen  to  fill  and  on  inspiration  to  empty, 
giving  the  appearance  of  a  pulse  to  this  respiratory 
variation  of  pressure.  For  about  an  inch  and  a  half 
above  the  thorax  the  suction  effect  of  the  intrathoracic 
neu.uive  pressure  is  so  great  as  to  cause  an  intravenous 
negative  pressure  of  a  slight  degree,  usually  only 
during  inspiration. 

A  true  venous  pulse  may  occur  under  two  condi- 
tions physiologically.  If  a  gland  such  as  the  submax- 
illary  is  stimulated  vigorously  to  increased  activity  the 
freedom  of  the  capillary  path  through  the  gland  is  so 
great,  «>wing  to  capillary  dilatation,  that  the  arterial 
pulse  i<  communicated  through  the  capillaries  and  ap- 
pear- in  the  veins  leaving  the  gland.  Owing  to  the 
absence  of  valves  at  the  entrance  of  the  venae  ca\;e 
into  the  rijrht  auricle  the  auricular  systole  causes  a  re- 


60  THE  CIRCULATION  OF  THE  BLOOD. 

gurgitation  of  blood  into  the  veins,  and  a  resulting 
venous  pulse  perceptible  for  a  distance,  which  depends 
upon  the  force  of  cardiac  contraction,  and  the  varying 
pressure  in  the  great  veins,  and  may  often  be  seen  high 
in  the  neck  in  the  external  jugular  vein. 


QUESTIONS  FOR  CHAPTER  II. 

What  determines  the  moment  at  which  the  cardiac  valve  open 
and  closes  ? 

"Why  are  the  auriculo-ventricular  and  semilunar  valves  neve] 
open  at  the  same  time  ? 

Does  blood  enter  or  leave  the  ventricle  in  the  interval  betwee 
the  first  and  second  heart-sounds  ? 

Does  blood  enter  or  leave  the  ventricle  in  the  interval  betweei 
the  second  and  first  sounds? 

If  the  auriculo-ventricular  valves  be  insufficient,  during  wha 
period  of  the  heart  cycle  will  blood  escape  from  the  ventricle  into 
the  auricle  ? 

If  the  aortic  valve  be  insufficient,  during  what  period  of  the 
cycle  will  blood  flow  back  from  the  aorta  into  the  ventricle? 

Of  what  accompanying  event  should  we  make  use  in  distin- 
guishing the  first  from  the  second  heart-sound  ? 

If  while  the  force  which  propels  liquid  through  a  tube  remains 
constant  the  resistance  be  varied,  how  is  the  expenditure  of  the  pro- 
pelling force  modified  ? 

Why  is  the  pressure  in  the  aorta  higher  than  that  in  the  small 
arteries? 

Which  travels  most  rapidly,  the  pulse  or  the  blood  stream  ? 

When  the  pulse  is  large,  what  is  the  condition  of  the  arterioles? 

When  the  heart  is  beating  strongly,  how  can  you  determine  the 
extent  of  vascular  tone? 

What  sort  of  pulse  accompanies  dyspnea  ? 

Why  should  the  dicrotism  of  the  pulse  be  exaggerated  when  the 
peripheral  resistance  is  low  ? 

What  different  circumstances  tend  to  the  production  of  a  capil- 
lary pulse  ? 

How  does  it  happen  that  not  only  the  auricle,  but  the  ventricle 


QUESTIONS.  61 

ill-..  brats  more  slowly  during  increased  activity  of  the  inhibitory 
center? 

What  is  the  result  of  inhibiting  the  cardio-inhibitory  center? 

Why  should  division  of  both  pueumogastric  nerves  lower  the 
pressure  in  the  large  veins? 

In  what  respect  would  the  regulation  of  the  blood  pressure  be 
modified  by  destruction  of  the  cardio-inhibitory  center? 

Why  should  compression  of  the  aorta  cause  the  heart  to  beat 
more  slowly? 

Through  what  two  channels  may  one  organ  influence  another? 

How  is  tin-  blood-flow  through  the  small  vessels  affected  by  loss 
of  arterial  elasticity? 

What  imiM>rtance  do  you  attach  to  the  position  of  a  patient  dur- 
ing chloroform  or  ether  anesthesia? 

( 'o  m  pa  re  the  effects  on  blood  pressure  of  the  division  of  the  spinal 
cord  in  the  cervical  and  in  the  lumbar  regions. 

How  many  neurones  are  concerned  in  the  control  exercised  by 
the  constrictor  center  over  a  single  arteriole? 

How  can  it  be  determined  whether  the  control  exercised  by  a 
center  is  continuous? 

How  does  bleeding  modify  vascular  tone? 

How  does  indirect  differ  from  direct  stimulation  of  a  center? 

What  conditions  of  the  circulatory  system  may  lead  to  fainting? 

Of  what  importance  is  the  iutracapillary  blood  pressure? 

It  all  the  nerves  of  a  limb  have  been  divided,  would  it  be  pos- 
sible, by  causing  the  muscles  of  this  limb  to  perform  work,  to  in- 
tluenee  the  heart-beat  ? 

How  does  severe  hemorrhage  cause  dilution  of  the  blood? 

How  does  a  rise  of  arterial  pressure  tend  to  concentrate  the 
blood? 

HO\N  does  the  concentration  of  the  blood  tend  toward  a  rise  of 
blood  pressure? 

What  nervous  meclianism  opposes  these  two  tendencies? 

In  what  particulars  is  the  existence  of  the  vasoconstrictor  center 
a  MM  nve  of  economy  to  the  body? 

What  different  vascular  conditions  may  lead  to  a  paling  of  the 

fare  •' 

What  class  of  vessels  is  the  seat  of  every  important  alteration  in 
the  composition  of  the  blood  ? 


62  THE  CIRCULATION  OF  THE  BLOOD. 


In  what  organ  is  lymph  most  rapidly  formed  ? 

In  the  absence  of  the  vasoconstrictor  center,  how  could  the  blood 
supply  of  a  given  organ  be  modified  according  to  its  needs  ? 

In  what  respect  would  the  regulation  of  the  blood  pressure  be 
interfered  with  by  division  of  both  depressor  nerves? 

Would  the  division  of  the  cervical  sympathetic  nerve  have  any 
effect  on  the  color  of  the  face  ? 

Would  you  class  the  vasodilators  as  vasomotor  nerves  ? 

Is  constant  standing  or  walking  the  more  productive  of  varicose 
veins  ? 

How  can  we  afford  the  greatest  voluntary  assistance  to  the  en- 
trance of  venous  blood  into  the  heart  ? 

Why  does  putting  a  cold  object,  such  as  a  key,  down  the  back 
tend  to  stop  epistaxis  ? 

How  are  the  lowTer  limbs  affected  by  compression  of  the  iliac 
veins? 

How  would  you  expect  the  size  of  the  heart  to  vary  during 
dyspnea  ? 

What  effect  on  intrathoracic  pressure  has  the  systole  of  the  ven- 
tricles ? 

If  the  heart  be  emptied  of  blood  and  be  caused  to  beat,  which 
of  the  heart-sounds  will  be  heard  ? 

How  do  you  know  that  the  slow  rate  of  blood-flow  through  the 
capillary  district  is  due  to  the  width  of  bed  and  not  to  resistance? 

Explain  the  occurrence  of  a  venous  pulse. 


CHAPTER  III. 

RESPIRATION, 

Tin-:  function  of  the  lungs  consists  in  the  exposure 
<>i'  i  In-  blood  to  the  air,  whereby  an  exchange  of  gases 
between  the  air  and  the  blood  is  rendered  possible. 
This  exposure  is,  however,  totally  ineffective,  the  lungs 
valueless,  unless  their  alveoli  are  constantly  ventilated. 
The  ventilation  of  the  lungs  is  accomplished  by  the 
n-piratory  muscles,  which  by  their  contraction  bring 
about  variation  in  the  capacity  of  the  thorax,  and  con- 
sequently in  that  of  the  lungs.  The  inner  surface  of 
the  lnn<r  and  the  outer  surface  of  the  thorax  are  both 

o 

exposed  to  the  atmospheric  pressure  ;  the  two  are  thus 
held  closely  in  contact  with  one  another  by  a  pressure 
of  fourteen  jxHinds  to  the  square  inch,  and  every  move- 
ment of  the  chest-wall  must  be  accompanied  by  a  sim- 
ilar expansion  or  diminution  of  the  lung.  Art  enlarge- 
ment of  the  thorax  will  therefore,  by  increasing  the 
rapaeity  of  the  lungs,  lower  the  pressure  within  them, 
and,  if  the  glottis  be  open,  lead  to  the  entrance  of  air. 
The  muscles  which  may  assist  in  the  enlargement  of 
tin-  thoracic  cavity  and  lungs,  and  thus  act  as  muscles  of 
inspiration,  are  the  diaphragm,  which  on  contraction 
increases  the  vertical  diameter  of  the  chest,  and  the 
>ealeni,  levatores  costarum,  serrati  postici  superiores, 
external  intereostals,  and  intercartilaginous  portion  of 
the  internal  intereostals,  which  all  take  part  in  raising 
the  ribs,  and  thus  increasing  the  lateral  and  antero- 

63 


64  RESPIRATION. 


posterior  diameters.     These  diameters  of  the  chest  are 
increased  by  raising  the  ribs,  owing  to  the  obliquity  of 
the  costo vertebral  hinge.     Quiet  expiration  is  accom-i 
plished,  without  the  aid  of  muscular  contraction,  by  the 
elastic  recoil  of  parts  which  are  distorted  during  inspi- 
ration, such  as  the  costal  cartilages,  the  abdominal  wall, 
and  the  lungs,  and  by  the  weight  of  the  ribs,  sternumj 
thoracic  muscles,  etc.     In   forced  expiration,  the  dia- 
phragm is  pushed  upward   by  the  abdominal  viscera*  | 
through  the  contraction  of  the  abdominal  muscles,  while 
the  ribs  are  drawn  downward  by  the  contraction  of  the 
triangulares  sterni,  interosseous  portion  of  the  internal 
intercostals,  etc. 

Even  when  the  inspiratory  muscles  are  at  rest,  there 
exists,  between  the  layers  of  the  pleurae,  a  negative 
pressure ;  that  is,  a  pressure  less  than  atmospheric  pres- 
sure.    This  is  due  to  the  fact  that  a  certain  amount  of 
the  atmospheric  pressure  is  consumed  in  holding  tin 
lung  in  contact  with  the  chest-wall,  the  remainder  be 
exerted,  through  the  lung,  against  the  inner  surface  oi 
the  thorax  and  the  outer   surface    of  the  heart  an( 
vessels.     The  lungs  are  not  large  enough  to  fill  th 
thoracic  cavity  unless  they  are  inflated,  and  their  infla 
tion  requires  a  small  amount  of  force.     If  the  inter 
pleural  pressure  be  measured  Avhen  the  respiratory  mus 
cles  are  quiescent,  or  after  death,  it  will  be  found  to  b 
about  754  mm.  of  mercury,  or  about  6  mm.  Hg  les 
than  atmospheric  pressure ;  a  negative  pressure,  then,  01 
6  mm.  Hg.     At  the  end  of  a  forcible  inspiration  the 
interpleural  pressure  may  fall  as  low  as  730  mm.  Hg, 
for  the  lungs  are  further  inflated  and,  of  course,  offer 
more  resistance  to  the  inflating  force — the  atmospheric 
pressure.     The  interpleural   pressure  is  always  lower 
than  the  intrapulmonary  pressure,  though  during  forci- 
ble expiration  it  may  rise  above  atmospheric  pressure, 


NEGATIVE  PRESSURE.  65 

If  the  < -hot-wall  be  pierced,  so  that  air  can  enter  the 
interplenral  space,  the  outer  as  well  as  the  inner  surface 
i»t'  the  lung  being  now  exposed  to  the  full  atmospheric 
piv— lire,  the  lung,  owing  to  its  own  elasticity,  will 
promptly  collapse.  If  both  sides  of  the  thorax  be 
perforated,  respiration  must  cease,  for,  since  the  elasticity 
of  the  lungs  will  resist  the  entrance  of  air,  through 
the  trachea,  into  themselves,  an  enlargement  of  the  chest 
will  onlv  result  in  the  entrance  of  air  into  the  inter- 
pleiiral  .-paces.  The  importance  of  the  interpleural 
negative  pressure,  in  respect  to  the  flow  of  blood  through 
the  vein-  into  the  "chest,  has  been  already  mentioned. 
The  outer  surface  of  the  heart  and  large  intrathoracic 
vessels  U  Mibjected,  when  the  thorax  is  at  rest,  to  a 
pie— me  of  only  754  mm.  Hg,  while  the  veins  which 
lie  outside  the  chest  are  exposed  to  the  full  atmospheric 
pie— me — 700  mm.  Hg ;  it  is  evident,  then,  that  blood 
will  be  forced  from  points  where  the  veins  are  more,  to 
a  point  where  they  are  less,  compressed.  Inspiration 
will  further  this  tendency;  expiration  will  lessen  it, 
and,  if  forcible,  will  prevent  the  entrance  of  blood. 

1 1 opi ration  may  seem  to  assume  one  of  two  types, 
diaphragmatic  or  costal,  but  under  normal  conditions 
of  l»odv  movements  both  the  diaphragm  arid  the  tho- 
racie  muscles  enter  into  every  respiratory  movement. 
I'o-iiinu  of  the  body,  clothing,  or  habit  may  modify 
the  normal  freedom  of  respiratory  movement,  and  it  i> 
.-••en  that  women  usually  breathe  more  costally  than 
diaphragrnatically,  and  that  the  reverse  is  true  with 
men. 

In  <juiet  breathing  the  chest  is  neither  expanded  nor 
contracted  to  the  full  extent  possible,  so  that  the  venti- 
lation of  the  lungs  is  not  so  complete  as  might  be.  The 
amount  of  air  ordinarily  inspired  and  expired  is  about 
500  c.c.,  and  is  known  as  the  tidal  air ;  in  addition  to 


66  RESPIRATION. 


this,  an  amount,  which  varies  with  the  capacity  of  the 
chest,  and  is  called  the  complemental  air,  can  be  in- 
spired, the  average  quantity  being  in  the  neighborhood  of 
1500  c.c.  After  the  expiration  of  the  tidal  air,  about 
1500  c.c.  more  may  be  expelled,  this  volume  being 
known  as  the  reserve,  or  supplemental  air.  These  three 
volumes  taken  together,  and  amounting  to  3500  c.c., 
are  called  the  respiratory,  or  vital,  capacity.  Not 
all  the  air  can  be  expelled  from  the  lungs ;  there 
remains  after  the  most  forcible  expiration  about  800 
c.c. — the  residual  air. 

The  division  of  the  cavity  of  the  lungs  into  innumer- 
able small  alveoli  enormously  increases  the  respiratory 
surface,  which  is  estimated  as  being  90  square  meters. 

On  its  way  through  the  upper  air-passages  the  tem- 
perature of  the  inspired  air  is  raised  or  lowered  to  that 
of  the  body  ;  it  is  moistened,  unless  already  saturated 
with  water  ;  and,  to  a  certain  extent,  purified  from  par- 
ticles of  foreign  matter  which  adhere  to  the  moist 
mucous  membrane,  and  are  carried  toward  the  mouth 
and  nose  by  the  movements  of  the  cilia. 

Respiration  may  be  divided  into  external  respiration, 
the  exchange  of  gases  between  the  air  and  the  blood 
which  occurs  in  the  lungs  ;  and  internal  respiration,  the 
exchange  of  gases  which  takes  place  between  the  blood 
and  lymph  and  the  tissues. 

External  Respiration. — Diffusion  goes  on  rapidly 
between  the  alveolar  air  and  the  tidal  air  that  is 
inspired,  the  latter  losing  oxygen  to  the  extent  of 
about  4J  volumes  per  cent.,  and  gaining  about  4 
volumes  per  cent,  of  carbon  dioxid.  The  ratio  existing 
between  the  amount  of  oxygen  which  disappears, 
and  the  volume  of  carbon  dioxid  which  appears,  is 
known  as  the  respiratory  quotient  ^.  The  respira- 


EXTERNAL  RESPIRATION.  67 

tory  quotient  indicates  the  extent  to  which  the  oxygen 
absorbed  is  used  in  the  oxidation  of  carbon ;  this 
varies  with  circumstances — for  example,  with  the 
diet.  On  a  purely  carbohydrate  diet  the  quotient  will 
approach  unity,,  for  sufficient  oxygen  is  contained  in  the 
carbohydrate  molecule  to  oxidize  its  hydrogen;  on  the 
other  hand,  a  fatty  diet  will  reduce  the  quotient,  for  in 
a  molecule  of,  for  instance,  stearin,  C3Hr)(ClsH.vO2)3, 
there  arc  110  atoms  of  hydrogen  to  but  6  of  oxygen. 
The  quotient  on  a  proteid  diet  is  intermediate  between 
the  two.  During  starvation  the  respiratory  quotient 
falls,  since  the  animal  lives  on  its  own  store  of  fat  and 
proteid,  the  amount  of  carbohydrate  in  the  body  being 
very  small.  Exercise  raises  the  quotient,  owing  to  the 
lad  that  muscular  work  is  done  for  the  most  part  at  the 
expense  of  carbohydrates. 

The  exchange  of  gases  which  occurs  between  the  air 
in  the  pulmonary  alveoli  and  the  blood  in  the  capillaries 
of  the  lung  is,  perhaps,  not  to  be  wholly  explained  by 
diffusion,  some  observers  having  found  the  tension  of 
oxygen  to  be  greater  in  arterial  blood  than  in  the 
alveoli  of  the  lungs;  this  is  the  opposite  of  what  we 
should  expect  as  the  result  of  simple  diffusion.  We 
may,  however,  assume  that  diffusion  is  the  main  factor 
in  the  exchange,  which  may  perhaps  be  furthered  by 
some  peculiarity  of  the  alveolar  membrane  which 
separates  the  air  from  the  blood. 

Hlood  plasma  absorbs  rather  less  oxygen  than  is 
taken  up  by  water;  blood,  however,  behaves  very 
differently,  for  on  being  shaken  with  air  it  may  absorb 
as  much  as  23  volumes  per  cent,  of  oxygen.  That 
tlii-  larire  quantity  is  not  held  simply  in  solution  is 
shown  by  subjecting  arterial  blood  to  an  atmosphere  in 
which  the  partial  pressure  of  oxygen  is  gradually 


68  RESPIKATION. 

reduced  ;  under  these  circumstances,  oxygen  is  slowly 
given  up  by  the  blood,  as  would  be  the  case  with  water ; 
but  when  the  partial  pressure  of  oxygen  has  been 
reduced  to  about  25  mm.  of  mercury,  if  the  blood  be 
at  body-temperature,  it  begins  to  come  off  very  rapidly, 
and  the  color  of  the  blood  changes  from  the  arterial  to 
the  venous  hue.  The  oxygen  is  for  the  most  part  held 
in  loose  chemical  combination  with  hemoglobin,  as 
oxyhemoglobin.  One  gram  of  hemoglobin,  at  0°  C.  and 
760  mm.  Hg  pressure,  unites  with  1.3  c.c.  oxygen  ;  it 
is  contained  in  blood  to  the  extent  of  about  14^. 
Arterial  blood  contains  about  20  volumes  per  cent, 
oxygen,  40  volumes  per  cent,  carbon  dioxid,  and  1  to  2 
volumes  per  cent,  nitrogen.  The  proportion  of  gases 
in  venous  blood  is  more  variable  ;  it  contains,  as  a  rule, 
10  volumes  per  cent,  oxygen,  47  volumes  per  cent, 
carbon  dioxid,  and  1  to  2  volumes  per  cent,  nitrogen. 
It  will  be  noticed  that  only  a  small  proportion  of  the 
carbon  dioxid  is  eliminated  as  the  blood  passes  through 
the  lungs,  and  that  only  about  half  the  oxygen  disap- 
pears from  the  arterial  blood  on  its  passage,  from  the 
arterioles  to  the  veins,  through  the  systemic  capillaries. 
Internal  Respiration. — The  cells  of  the  various 
tissues  prevent  the  accumulation  of  oxygen  in  the 
lymph  which  surrounds  them ;  they  display  a  great 
avidity  for  oxygen  and  take  it  up  as  fast  as  it  reaches 
them,  thus  maintaining  in  the  lymph  a  practical  oxygen 
vacuum.  Consequently,  a  rapid  diffusion  of  oxygen 
must  occur,  through  the  capillary  wall,  from  the  plasma 
to  the  lymph ;  and  as  the  partial  pressure  of  oxygen 
diminishes  in  the  plasma,  the  oxyhemoglobin  of  the  red 
cells  must,  to  a  certain  extent,  be  reduced.  Oxygen  will 
pass  from  the  blood-cells  to  the  plasma,  and  from  the 
plasma  into  the  lymph,  thus  reaching  the  tissue  cells.  The 


INTERNAL  RESPIRATION.  69 

individual  capillaries  are,  however,  so  short  that  each  red 
cell  remains  in  this  district  but  a  brief  period,  and  time  is 
not  given  for  the  reduction  of  all  its  oxyhemoglobin  ;  still 
more  is  this  the  case  when  the  arterioles  of  an  active 
organ  are  dilated,  and  the  blood  flows  through  its  capil- 
laries with  increased*  celerity.  Under  these  circum- 
stances a  larger  number  of  red  cells  will  pass  through 
each  capillary  in  a  given  time,  and  though,  in  the 
aggregate,  more  oxygen  will  be  given  up  to  the  lymph, 
each  cell  will  part  with  a  smaller  quantity  than  usual, 
and  the  blood  reaching  the  veins  will  retain  its  arterial 
color. 

It  is  not  to  be  supposed  that  the  oxygen  is,  on  reach- 
ing the  cells  of  the  various  tissues,  immediately  com- 
bined with  carlxm  to  form  carbon  dioxid  ;  it  seems 
rather  to  be  stored  within  the  cell  in  some  more  com- 
plex combination,  which  later  on  breaks  down,  with  the 
liberation  of  carbon  dioxid.  Muscle,  for  example,  may 
be  caused  to  contract,  and  to  perform  a  considerable 
amount  of  work,  in  the  absence  of  free  oxygen,  giv- 
ing off  meanwhile  carbon  dioxid,  wrhich  can  only  have 
originated  by  the  break-down  of  some  oxygen-contain- 
ing substance,  possibly  of  phosphocarnic  acid,  within 
the  muscle. 

The  carbon  dioxid  thus  formed  by  the  cells  passes 
into  the  lymph  ;  it  accumulates  here,  and  since  the  par- 
tial pressure  of  carbon  dioxid  is  higher  in  the  lymph 
than  in  the  blood  plasma,  it  diffuses  from  the  former 
into  the  latter.  Only  a  small  proportion  of  the  carbon 
dioxid  carried  in  the  venous  blood  is  in  simple  solution, 
a  rather  larger  proportion  is  in  firm  chemical  combina- 
tion, and  the  majority  in  loose  chemical  combination  in 
the  plasma  ;  a  small  quantity  only  is  held  in  chemical 
combination  in  the  corpuscles.  On  reaching  the  lungs 


70  RESPIRATION. 

the  carbon  dioxid  diffuses  from  the  blood,  where  its 
partial  pressure  is  high,  into  the  air-spaces,  where  its 
partial  pressure  is  low  ;  as  before  stated,  only  about 
one-fifth  of  the  carbon  dioxid  contained  in  venous  blood 
is  eliminated  in  this  way.  The  setting  free  of  carbon 
dioxid  by  the  splitting-up  of  Na'HCO3,  in  which  com- 
bination most  of  the  CO2  of  the  plasma  is  held,  is 
brought  about  by  the  action  of  substances,  oxyhemo- 
globin  and  globulins,  which  act  as  weak  acids. 

Nervous  Control. — The  respiratory  muscles  are  under 
the  control  of  the  respiratory  center,  which  is  situated  in 
the  spinal  bulb ;  in  the  neighborhood,  therefore,  of  the  im- 
portant centers  which  govern  the  circulation.  The  respi- 
ratory center  is  bilateral,  but  the  two  halves,  connected  by 
commissural  fibers,  act  in  unison.  It  is  rhythmically 
active,  ordinarily  at  the  rate  of  from  fifteen  to  twenty  res- 
pirations per  minute,  the  respiratory  rhythm  usually  vary- 
ing with  the  heart  rhythm  as  one  to  four.  This  center  is 
exceedingly  sensitive  to  nerve  impulses  which  reach  it 
from  the  periphery  or  from  the  higher  centers  in  the  brain, 
and  to  changes  in  the  chemical  composition  of  the  blood. 
The  nerve-fibers  emanating  from  the  respiratory  center 
pass  downward  into  the  spinal  cord  without  crossing  the 
median  line,  and  end,  in  the  gray  matter  of  the  cord,  in 
the  neighborhood  of  the  motor  nerve-cells  which,  situ- 
ated in  the  different  regions  of  the  cord,  innervate  the 
respiratory  muscles.  The  center  also  dispatches  im- 
pulses to  the  nuclei  of  some  of  the  motor  cranial  nerves, 
and  thus  governs  accessory  respiratory  movements  which 
accompany  inspiration,  such  as  those  of  the  vocal  cords 
and  alse  nasi.  Although  each  half  of  the  center 
controls  the  respiratory  muscles  situated  on  the  same 
side  of  the  body  as  itself,  the  nervous  impulses  which  it 
discharges  may,  under  certain  circumstances,  after  de- 


NERVOUS  CONTROL.  71 

the  cord,  cross  over  to  the  opposite  side  and 
about  the  contraction  of  contra  lateral  muscles. 
Destruction  of  the  center  puts  an  end  to  respiration  and 
proves  fatal.  Division  of  the  spinal  cord  just  below  the 
origin  of  the  phrenic  nerve  causes  paralysis  of  the  tho- 
racic and  abdominal  muscles  concerned  in  respiration, 
but  the  diaphragm,  innervated  through  the  phrenic 
nerve,  remains  active.  Division  of  the  cord  above  the 
origin  of  the  phrenic  nerve  proves  as  fatal  as  destruc- 
tion of  the  respiratory  center,  though  life  may  be  sup- 
ported for  half  an  hour  or  so  by  the  contractions  of  the 
sternocleidomastoids,  innervated  through  the  spinal  ac- 
<v»ory  nerve. 

( )f  the  various  stimuli  to  which  the  center  is  respon- 
HVC,  the  condition  of  the  blood  is  the  most  important. 
A  venous  condition  of  the  blood  acts  as  a  strong  stimu- 
lus to  the  respiratory  center;  consequently,  it  is  impos- 
sible  to  voluntarily  cease  breathing  for  long  at  a  time. 
It  is  easy  to  inhibit  the  center  and  prevent  its  response 
up  to  a  certain  point,  but  as  the  blood  becomes  more 
and  more  venous,  the  stimulation  of  the  center  grows  so 
forcible  that  it  overcomes  our  most  strenuous  efforts  at 
inhibition,  and  we  begin  to  breathe  in  spite  of  ourselves. 
If  the  blood  i*  lacking  in  oxygen  the  inspiratory  phase 
of  respiration  will  be  increased,  and  if  there  is  an  ex- 
cess of  carbon  dioxid  the  expiratory  phase  will  be  in- 
cn-a-ed,  thus  Diving  evidence  that  the  bilateral  respira- 
tory center  has  an  inspiratory  and  an  expiratory  portion 
which  respond  to  appropriate  stimulation. 

Dyspnea,  or  difficult  and  labored  breathing,  may  re- 
Mi  It  from  chemical  or  mechanical  interference  with  a 
Mipply  of  blood  to  the  respiratory  center  sufficient  in 
quantity  and  with  a  sufficient  degree  of  purity  and 
content.  Thus  we  may  have  hemorrbagic  <T 


72  RESPIRATION. 

cardiac  dyspnea,  due  to  lack  of  bulk  of  blood,  or  force 
of  blood  sufficient  to  give  a  free  circulation  in  the  brain, 
or  "  O-dyspnea,"  due  chiefly  to  a  lack  of  oxygen,  and 
"CO2-dyspnea,"  due  to  an  excess  of  carbon  dioxid  in  the 
circulating  blood.  The  center  is  also  sensitive  to  changes 
in  the  temperature  of  the  blood,  a  rise  increasing,  a  fall 
lessening,  its  activity.  As  in  the  case  of  the  cardio- 
augmentor  center,  the  waste  products  of  active  muscular 
metabolism  serve  as  a  stimulus ;  exercise  is  accompanied 
by  an  increased  rate  and  depth  of  respiration.  Almost 
as  important  as  the  stimulus  afforded  by  the  lack  of  oxy- 
gen or  excess  of  carbon  dioxid  is  the  influence  exerted 
over  the  center  by  afferent  nerve  impulses.  We  may 
assume  that  the  respiratory  center,  deprived  of  all  stim- 
uli, would  cease  to  act ;  in  other  words,  that  it  is  not 
spontaneously  active. 

The  respiratory  center  may  be  stimulated  through 
almost  any  afferent  nerve,  those  Avhich,  in  relation  to 
this  center,  are  of  most  importance  being  the  afferent 
nerves  of  the  respiratory  tract.  Division  of  both  vagi 
results  in  a  lessened  frequency  and  increased  depth  of 
respiration,  owing  to  the  absence  of  afferent  impulses 
which,  in  the  normal  course  of  events,  arising  in  the 
lungs  and  reaching  the  center  through  the  vagi,  in  some 
way  quicken  its  activity.  The  pulmonary  terminations 
of  these  nerve-fibers  seem  to  be  stimulated  either  by  the 
inflation  or  by  the  collapse  of  the  lung,  or  by  both.  If, 
the  vagi  being  intact,  a  sudden  collapse  of  the  lung  be 
caused,  there  results  a  contraction  of  the  diaphragm ;  if 
the  lungs  be  suddenly  inflated,  the  result  is  a  relaxation 
of  the  diaphragm.  One  or  other  of  these  events  is  re- 
flex ;  possibly  both.  Whether  the  impulses  concerned 
are  inhibitory  to  the  respiratory  center  or  result  in  its 
stimulation  is  uncertain. 


NERVOUS  CONTROL.  73 

The  inferior  or  recurrent  laryngeal  nerves  are  pure 
motor  nerves  to  the  muscles  of  the  larynx.  The  supe- 
rior laryngeal  nerves  are  motor  for  the  cricothyrokl 
muscle  and  sensory  for  the  mucous  memhrance  of  the 
glottis  and  the  larynx.  Stimulation  of  the  superior 
lary ii^cal  nerves  results  in  a  cessation  of  respiration, 
followed,  as  a  rule,  by  an  expiratory  effort,  thus  imitat- 
ing the  chain  of  events  following  the  presence  of  an 
irritating  gas  or  foreign  substance  at  the  entrance  of  the 
larvnx  ;  /.  e.f  holding  the  breath  and  then  coughing. 
If  the  inferior  laryngeal  nerves  are  cut,  the  closure  of 
the  glottis  and  the  explosive  expiration  do  not  occur, 
the  a pnea  followed  by  expiratory  effort  being  the  only 
results  of  superior  laryngeal  nerve  stimulation  when  the 
laryngeal  muscles  are  paralyzed.  Coughing  may  also 
re.-ult  from  irritation  of  the  afferent  fibers  of  the  vagus 
in  the  lungs,  stomach,  or  liver.  Sneezing  closely  re- 
><  inbles  coughing,  save  that  part  of  the  air  is  expelled 
through  the  nose,  and  may  be  excited  by  stimulation  of 
the  nasal  branch  of  the  fifth  cranial  nerve,  or  through 
the  c licet  of  a  bright  light  on  the  retina.  The  reflex 
ga>p  which  is  excited  by  entering  cold  water  is  familiar 
to  all.  During  swallowing,  respiration  is  stopped  by 
inhibit  ion  of  the  respiratory  center  through  the  glosso- 
pharyngeal  nerve,  the  pharyngeal  terminations  of  which 
arc  -t  imnlated  by  the  substance  swallowed,  thus  affording 
a  mechanism  which  prevents  the  inhalation  of  food  into 
the  trachea.  The  center  may  also  be  inhibited  on  the 
introduction  of  irritating  gases  into  the  nasal  fossae,  the 
terminations  of  the  fifth  cranial  nerve  being  thus 
stimulated;  the  same  effect  may  be  produced  by  the 
inhalation  of  licjuid.  As  is  well  known,  the  emotions 
have  a  marked  influence  over  the  depth  and  rate  of 
respiration,  and  may  cause  its  temporary  arrest.  The 


74  RESPIRATION. 

respiratory  center  is  also  under  the  control  of  the  will, 
though  it  cannot  be  thus  inhibited  indefinitely. 

When  the  proper  arterialization  of  the  blood  is  pre- 
vented, hyperpnea,  or  increased  depth  and  frequency  of 
respiration,  ensues ;  if  this  does  not  result  in  the  access 
of  oxygen  to  the  required  extent,  or  in  the  removal  of 
the  surplus  carbon  dioxid,  or  both,  there  follows  more 
exaggerated    breathing,     dyspnea,    in    which    forcibl 
expiration  predominates.     If  the  struggle  still  prov 
ineffectual,     convulsions    intervene,    giving    place 
exhaustion,  a  few  long-drawn  inspirations,  and  death 

Apnea,  or  temporary  cessation  of  breathing,  may 
induced  by  rapid  artificial  respiration ;  this,  in  the 
normal  animal,  is  not  due  to  overoxygenation  of  the 
blood,  for  the  blood  will  take  up  little  more  oxygen 
than  usual  when  pure  oxygen  is  breathed,  and  the  same 
condition  is  produced  if  hydrogen  be  used  for  inflating 
the  lungs.  It  is  caused  by  the  effect  produced  on  the 
respiratory  center  through  the  afferent  fibers  of  the 
vagus,  the  pulmonary  terminations  of  which  are  stimu- 
lated by  the  rapidly  repeated  distention  and  collapse  of 
the  lungs.  If  both  vagi  have  previously  been  divided, 
it  is  more  difficult  to  induce  apnea,  and  impossible  by 
the  use  of  hydrogen ;  in  this  case,  it  is  probably  due  to 
a  better  arterialization  of  the  blood,  which,  after  division 
of  the  vagi,  has  become  defective. 


QUESTIONS  FOR  CHAPTER  III. 

If  a  cannula  which  is  connected  with  a  mercury  manometer  be 
thrust  through  the  chest-wall  without  injuring  the  lung,  in  which 
direction  will  the  mercury  move  ? 

Under  what  circumstances  will  the  movement  of  the  mercury  be 
greatest  ? 

Is  the  interpleural  pressure  ever  positive  ? 


nlMSTIONS.  75 

What  force  resists  the  expansion  of  the  thorax  when  tin-  glottis 
is  rl.tsed? 

Does  the  elasticity  of  the  lungs  aid  in,  or  oppose,  inspiration? 

H<>\\  is  the  color  of  the  face  affected  by  a.  fit  of  coughing,  and 
\\hat  is  the  mechanism  concerned? 

Why  is  it  impossible  to  voluntarily  empty  the  lungs? 

What  force  causes  air  to  enter  the  lungs  during  inspiration? 

Is  it  possible  for  a  contraction  of  the  diaphragm  to  cause  e.xpi- 
rat  ion  ? 

What  \\onld  be  the  result  of  replacing  the  blood  by  serum? 

What  causes  a  newly  born  animal  to  breathe? 

What  causes  the  reduction  of  oxy hemoglobin  in  the  systemic 
capillaries? 

Ho\\  is  it  that  blood  leaving  an  active  organ  may  in  color 
resemble  arterial  blood  ? 

What  are  the  direct  and  indirect  effects  of  lack  of  oxygen  ? 

1  iocs  the  blood  undergo  purification  on  its  passage  through  the 
heart  ? 

Why  is  it  dangerous  to  breathe  coal-gas? 

Is  the  color  of  venous  blood  due  to  the  presence  of  an  excess  of 
ear'uoii  dioxid? 

(Jive  the  causation  and  describe  the  occurrence  of  dyspnea. 

The  spectra  of  oxyhemoglobin  and  carl>on  monoxid  hemoglobin 
an-  \ery  similar.  How  can  these  two  substances  l>e  most  readily 
distinguished  from  each  other? 

Which  of  the  effects  of  destroying  the  spinal  bulbxire  immedi- 
ately fatal? 

What  is  the  effect  of  separating  the  two  halves  of  the  medulla 
by  a  median  incision? 

M\ plain  the  result  of  introducing  a  foreign  body  into  the 
larynx. 

How  is  this  effect  modified  after  division  of  the  spinal  cord  at 
the  le\.  1  of  the  seventh  cervical  nerves? 

Of  what  importance  is  the  stimulation  of  the  medullary  centers 
by  the  \\aste  products  of  muscular  activity  ? 

How  does  biting  the  lip  stop  sneezing? 

Why  are  the  lungs  lass  well  protected  after  division  of  the  glos- 
sopharyn.ueal  nerves? 

Why  is  it  dangerous  to  divide  the  laryngeal  nerves? 


76  RESPIRATION. 

Curari   paralyzes  the  skeletal  muscles.      How  does  it  cause 
death? 

Why  is  paralysis  of  the  expiratory  less  injurious  than  that  of 
the  inspiratory  muscles  ? 

Why  is  ventilation  necessary  ? 

How  does  the  contraction  of  the  bronchial  muscles  affect  respi- 
ration ? 

Why  is  the  respiratory  quotient  of  a  herbivorous  animal  mod 
fied  by  starvation  ? 


CHAPTER  IV. 

DIGESTION* 

DIGESTION  consists  in  the  physical  and  chemical  al- 
tcration  of  food,  the  resulting  products  being,  as  a  rule, 
IIHMV  easily  absorbed,  and  in  some  cases  more  readily 
a— iinilated,  than  the  food-stuffs  as  they  are  originally 
taken.  In  order  that  it  may  be  absorbed,  food  must  be 
soluble,  though  it  is  possible,  but  highly  improbable, 
that  fats  form  an  exception  to  this  rule. 

Much  of  our  food  is  taken  in  a  form  that  requires 
mechanical  subdivision  ;  this  is  accomplished  by  the 
teeth  and  tongue,  and  by  the  movements  of  the  stomach. 
The  soluble  portion  of  the  food  that  happens  to  betaken 
in  solid  form — for  instance,  cane-sugar — is  readily  dis- 
solved in  the  saliva  or  gastric  juice,  but  insoluble  food- 
-t i ill's  must  of  necessity  undergo  some  change  in  com- 
position, and  this  is  brought  about  by  the  various  en- 
zymes, or  ferments,  which  are  secreted  by  thexglands  of 
the  alimentary  canal,  or  by  bacteria  which  are  constantly 
pi  (-nit  in  the  intestine. 

Our  food  consists  of  a  mixture  of  various  substances, 
tin-  most  important  of  which  are  proteids,  albuminoids, 
carbohydrates,  fats,  water,  and  inorganic  salts.  Pro- 
trid<  arc  essential,  though  taken  alone  they  form  neither 
a  suitable  nor  economic  diet.  In  discussing  the  diges- 
tion of  these  food-stuffs  it  will  be  well  to  treat  them 
Separately. 

Digestion  of  Carbohydrates. — On  introduction 
of  the  food  into  the  mouth  it  is  subjected  to  the 

77 


78  DIGESTION. 

influence  of  the  saliva,  with  Avhich  it  is  mixed  by 
movements  of  the  tongue  and  lower  jaw.  Here  begins 
the  solution  of  those  food-stuffs  which  are  soluble 
in  water.  That  part  of  digestion  which  consists  of 
chemical  change  also  begins  in  the  case  of  cooked 
starch  and  the  dextrins.  Uncooked  starch  is  insoluble ; 
it  exists  in  the  form  of  granules  covered  with  envelopes 
of  cellulose,  which  is  also  insoluble,  and  which,  though  it 
belongs  to  the  starch  group  of  carbohydrates,  is  not  at- 
tacked by  the  enzymes  of  the  alimentary  canal ;  it  passes 
unchanged  through  the  mouth  and  stomach  into  the  in- 
testine, where  a  part  of  it  is  acted  on  by  bacteria.  The 
cooking  of  starch  breaks  open  the  cellulose  envelopes,  and 
the  starch,  rendered  partly  soluble,  is  set  free.  There  is 
contained  in  saliva  an  enzyme,  ptyalin,  which  is  manu- 
factured by  the  salivary  glands,  and  which  is  amyloly  tic ; 
that  is,  it  brings  about  the  hydrolysis  of  starch.  By  this 
ferment  starch  is  converted  into  soluble  starch  or  ahiylo- 
dextrin.  The  soluble  starch  is  further  split  up  into  dex- 
trin and  malt-sugar  ;  the  dextrin  thus  formed  also  under- 
goes hydrolysis,  being  converted  into  a  simpler  form  of 
dextrin  and  maltose.  The  final  product  is  maltose,  but 
before  the  series  of  reactions  ends  there  probably  are  a 
number  of  different  dextrins  formed ;  each  one,  in  turn, 
being  split  up  with  the  formation  of  a  simpler  dextrin  and 
malt-sugar.  The  formula  (CgH10O5)n  is  used  to  represent 
each  member  of  the  starch  group.  Supposing,  for  the 
sake  of  simplicity,  that  the  true  formula  for  soluble 
starch  is  (C6H10O5)30,  as  has  been  stated,  then  the  series 
of  changes  which  occur  may  be  represented  by  the  fol- 
lowing equations  : 

(1)  3  (C6H1005)30  +  H20  =  (C6H1005)28  +  CHHnOn. 

Sol.  Starch  Dextrin  Maltose 

(2)  (C6H1005)28  +  H20  =  (C6H1005)26  +  C12H220U. 

Dextrin  Dextrin  Maltose 


DIGESTION  OF  CARBC  >  1 1  VI U  i  ATES.  7!) 

(:«)     (C6H1005)26  +  HaO  =  (C6HI005)24  +  C^Ou. 

I  '.-x triii  Dexlriu  Maltose 

an<l  H»  on  to  the  last  of  the  series : 

(15)     (C6H10()5)2     +     H,0    :   :    CuHaOn. 

Dextrin  Maltose 

Accord  ing  to  some  observers,  another  form  of  sugar, 
isomaltose,  appears  during  the  hydrolysis  of  starch,  but 
is  converted  into  maltose.  We  can  distinguish  two 
varieties  of  dextrin  by  their  behavior  with  iodin  :  ery- 
throdextrin  gives  with  iodin  a  red  color  reaction,  which 
disappears  on  heating  and  reappears  on  cooling  ;  achroo- 
<  lex  trin  is  so  called  because  it  gives  no  color  reaction  on 
treatment  with  iodin.  Starch  gives  a  dark  blue  color 
with  iodin.  Ptyalin  is  sensitive  to  a  change  in  reac- 
tion ;  it  acts  best  in  neutral  or  slightly  alkaline  solu- 
tion, and  its  action  is  prevented  by  the  presence  of  a 
trace  of  free  mineral  acid.  The  gastric  juice  contains 
hydrochloric  acid,  but  at  the  beginning  of  digestion  this 
i-  combined  with  the  proteids  that  enter  the  stomach, 
and  in  this  condition  does  not  prevent  the  action  of 
ptyalin,  though  it  reddens  litmus.  Saliva  that  is  swal- 
lowed and  enters  the  stoniach  may,  therefore,  continue 
to  act  upon  starch  and  dextrius  for  half  arf  hour  or 
more,  after  the  beginning  of  a  meal,  until  there  is  a 
.-urplus  of  HC1  which  is  uncombined  with  proteid  ; 
when  this  occurs,  the  action  of  pytalin  must  cease. 
That  portion  of  the  starch  and  dextrins  which  is  not 
digested  by  saliva,  either  in  the  mouth  or  stomach, 
pa»e>  into  the  intestine.  The  pancreatic  juice  contains 
an  cn/ynie,  amylopsin,  which  closely  resembles  pytalin 
in  it>  action,  and  may  be  identical  with  it.  Not  only 
does  the  amylopsin  convert  the  dextrins  and  cooked 
March  which  may  have  escaped  salivary  digestion  into 
maltose1,  but  it  also  brings  about  the  same  changes  in 


80  DIGESTION. 

any  raw  starch  that  has  been  liberated  from  its  cellulose 
covering  through  the  action  of  bacteria.  Probably  none 
of  the  starch  or  dextrin  which  enters  the  intestine  is 
absorbed  before  undergoing  digestion,  for  amylopsin 
acts  rapidly  and  powerfully,  but  it  is  possible  for  both 
these  substances  to  be  absorbed  as  such  in  the  large  in- 
testine. So  far,  then,  we  have  found  that  starch  is  con- 
verted by  digestion  into  maltose,  a  sugar  which,  although 
capable  of  being  absorbed,  is  of  no  value  as  such  to  the 
organism ;  if  it  enters  the  blood  as  maltose,  it  is  ex- 
creted by  the  kidneys.  Yet  it  is  very  unusual  to  find 
maltose  in  the  urine,  for  the  maltose  which  happens  to 
be  absorbed  by  the  epithelial  cells  which  line  the  stom- 
ach and  intestines  is  converted,  before  it  reaches  the 
blood,  probably  by  the  action  of  an  enzyme  contained 
within  the  cells,  into  dextrose.  This  change  also  occurs : 
within  the  stomach  under  the  influence  of  hydrochloric 
acid,  one  molecule  of  maltose  being,  by  hydrolysis,  con-^1 
verted  into  two  molecules  of  dextrose.  The  succus  en- 
tericus,  or  intestinal  juice,  contains  an  enzyme,  invertin, 
which  brings  about  the  same  change.  Cane=sugar  is 
acted  on  by  neither  pytalin  nor  amylopsin  ;  like  mal- 
tose, it  is  of  no  value  to  the  body  until  it  has  been  di- 
gested, though  it  may  be  absorbed.  After  eating  very 
large  quantities  of  cane-sugar  a  very  small  amount  may 
be  found  in  the  urine,  but  the  majority  is  hydrolyzed 
before  or  during  absorption ;  the  change  occurs  either 
in  the  stomach  through  the  action  of  hydrochloric  acid, 
in  the  intestines  under  the  influence  of  invertin,  or  dur- 
ing its  passage  through  the  epithelial  cells.  The  nature 
of  the  change  is  as  follows  : 

C12H220lt  +  H20  ±=  C6H1206  +  C6H1206. 
Cane-sugar  Dextrose      •     Levulose 

Both   dextrose  and   levulose  are  assimilable  ;   that  is, 
they  can  be  utilized  by  the  bioplasm.     Lactose,  or  milk- 


DIGESTION  OF  CARBOHYDRATES.  81 

sugar,  is  another  disaccharid  which  is  acted  on  in  the 
same  way  in  the  intestine,  but  not  in  the  stomach  ;  the 
change  is  as  follows  : 

Cl2H22On  +  H20  =  C6H1206  +  C6H1306. 
Milk-sugar  Dextrose          Galactose 

Not  all  the  dextrose  which  is  taken  with  the  food  or 
is  formed  during  digestion  reaches  the  blood;  a  variable 
<|iiantity  becomes  the  prey  of  bacteria.  This  may  occur 
in  the  mouth,  if  the  sugar  is  retained  between  the  teeth; 
in  the  stomach,  during  the  period  when  there  is  no  free 
hydrochloric  acid  present;  or  in  the  intestines,  which 
constantly  contain  bacteria.  The  main  result  of  this 
bacterial  decomposition  is  the  formation  of  lactic  acid. 
The  lactic  acid  bacillus  not  only  acts  on  sugar,  but  at- 
tacks starch  and  the  dextrins  also,  probably  first  con- 
verting these  into  dextrose,  and  the  dextrose  into  lactic 
acid.  The  destruction  of  the  enamel  of  the  teeth  is  due 
to  the  formation  of  lactic  acid  in  this  way.  The  lactic 
acid  may  be  partly  converted  into  butyric  acid  by  the 
fiirt her  action  of  bacteria.  Another  product  of  the  de- 
composition of  carbohydrates  by  bacteria  in  the  intestines 
is  alcohol,  which  is  formed  in  small  quantities  only. 
This  is,  of  course,  absorbed  together  with  the  lactic  acid, 
and  oxidized  in  the  system.  The  succus  entericus,  or 
intestinal  juice,  which  is  secreted  by  the  simple  glands 
of  the  intestinal  mucous  membrane,  exerts  a  very  feeble 
diastatic  action,  slowly  converting  starch  into  sugar;  it 
also  inverts  cane-sugar  into  dextrose  and  levulose ;  con- 
verts maltose  into  dextrose,  and  lactose  into  dextrose 
and  galactose.  Much  of  the  cellulose  escapes  bacterial 
decomposition  and  appears  in  the  feces.  The  starch  and 
dextrins  which  on  introduction  into  the  large  intestine 
may  be  absorbed  without  previous  change  are  evidently 
digested  on  their  way  through  the  epithelium,  for  they 
do  not  appear  in  the  blood. 


82  DIGESTION. 

TABLE  3.— DIGESTION  OF  STARCH. 


ymph  and 
blood 


Cellulose  Starch 

a.  b.         raw          cooked 


Marsh-gas, 
etc. 


a.        b.         c. 

t 
Maltose  J    b. 


Gastric  epi- 
tlielium 


(abgorbe(1) 


Sol.  starch 
a.          h. 

Dextrins 
a.       b. 


-^-Dextrose.... 


Intestinal 
epithelium 


Maltose-^ 


a. -^-(absorbed). 


Lactic  acid,  butyric  acid,  alcohol,  etc.  (absorbed) 


-^-Dextrose.. 


4~ 


..ympli  and 
blood 


DIGESTION  OF  PROTEIDS.  83 

Iii  Table  3  the  double  dotted  line  represents  the  pylo- 
ru> ;  above  these  lines  are  shown  the  changes  undergone 
by  starch  and  its  products  in  the  stomach,  the  change 
beginning,  however,  in  the  mouth.  Below  these  lines 
an-  -riven  the  changes  which  occur  in  the  intestines. 
The  different  agencies  through  which  these  reactions  are 
effected  are  mentioned  above,  in  the  text. 

Digestion  of  Proteids. — Proceeding  to  the  digestion 
of  another  group  of  food-stuffs,  namely,  the  proteids,  we 
have  tn  do  with  substances  the  majority  of  which  are 
1 1  in  re  complex  than  even  starch.  Of  their  structural 
formulae  we  have  no  knowledge.  As  their  name  in- 
dicates, they  are  the  most  important  of  the  food-stuffs, 
without  a  supply  of  which  life  cannot  be  supported 
for  any  considerable  time.  Their  chief  characteristics 
have  been  already  mentioned. 

Uncooked  proteids  and  those  which  are  not  rendered 
insoluble  by  heat  may,  if  given  in  the  solid  form,  be 
dissolved  in  the  saliva.  Saliva,  however,  contains  no 
prote<  >\yt\c  enzyme ;  it  is  incapable  of  bringing  about 
any  chemical  change  in  the  proteids,  which,  conse- 
quently, suffer  no  digestion  before  they  reach  the 
stomach,  though  they  may,  if  long  retained  within  the 
mouth, — for  instance,  between  the  teeth, — undergo  bac- 
terial decomposition.  Although,  like  soluble  starch, 
the  soluble  native  proteids  may,  to  a  certain  extent,  be 
absorbed  from  the  intestine  without  first  undergoing 
digestion,  the  absoqrtion  of  the  products  of  proteid 
digestion  goes  on  much  more  rapidly  ;  coagulated  pro- 
teids  are  altogether  incapable  of  being  absorbed  until 
they  have  been  converted  into  a  soluble  form.  Our 
knowledge  of  the  changes  which  proteids  undergo  during 
digestion  is  even  less  exact  than  in  the  case  of  carbo- 
hyd  rates,  but  it  seems  highly  probable  that  here,  too,  we 
have  a  series  of  hydrolytic  reactions,  the  original  mole- 


84  DIGESTION. 

cule  of  native  proteid  being  hydrated  and  split  up  into 
simpler  and  more  stable  substances.  In  support  of  this 
view  it  may  be  mentioned  that  the  same  products  result 
from  the  treatment  of  proteids  with  hydrolyzing  agents, 
such  as  boiling  mineral  acids  or  superheated  steam. 

On  entering  the  stomach,  proteids  are  subjected  toi 
the  influence  of  the  gastric  juice,  the  important  constit- 
uents of  which  are  pepsin,  hydrochloric  acid  Q.2fc, 
renuin,  water,  and  inorganic  salts. 

The  first  recognizable  step  in  the  digestion  of  the 
native  proteids  is  their  conversion  into  a  form  which, 
unless  first  precipitated  by  neutralization,  is  uncoagu- 
lable  by  heat.  For  example,  egg-albumen  is  converted 
by  pepsin  (the  proteolytic  enzyme  of  gastric  juice) 
and  hydrochloric  acid,  or  more  slowly  by  the  action 
of  hydrochloric  acid  alone,  into  an  album inate — acid 
albumin.  If  a  digestion  which  contains  albuminate 
be  neutralized,  a  precipitate  is  formed  which  consists 
of  albuminate,  and  is  called  a  neutralization  precipi- 
tate ;  if  an  excess  of  alkali  be  added,  the  albuminate 
redissolves,  as  an  alkali  albumin.  Albumin  that  has 
been  coagulated  by  boiling  is  by  pepsin  and  hydro- 
chloric acid  converted  into  soluble  albuminate,  but  the 
change  is  less  rapid  than  in  the  case  of  soluble  albumins. 
All  the  native  proteids  may  be  acted  on  in  this  way. 
As  gastric  digestion  progresses,  the  albuminates  are  con- 
verted into  proteoses,  and  these  into  peptones.  The 
solubility  of  the  proteid  increases  as  it  passes  from  one 
form  to  the  next ;  at  the  same  time,  its  power  of  dif- 
fusing through  animal  membranes  increases.  Native 
proteids  and  albuminates  are  nondialyzable ;  proteoses 
are  very  slightly  dialyzable,  peptones  distinctly  so, 
though  they  pass  through  membranes  much  more  slowly 
than  do  the  simpler  crystalloids.  This  probably  de- 
pends upon  the  large  size  of  the  proteid  molecule. 


DIGESTION  OF  PROTEIDS.  85 

Pepsin  is  incapable  of  causing  proteolysis  in  neutral 
or  alkaline  solution  ;  it  requires  the  presence  of  an  acid, 
hydrochloric  acid  being  the  most  favorable  to  its  action. 
It  is  quickly  destroyed  by  alkalies,  and  acts  less  rapidly 
when  neutral  salts,  such  as  sodium  chlorid,  are  present. 

Peptones  are  the  final  products  of  gastric  digestion, 
In  it  thcv  may  undergo  further  change  on  reaching  the 
intestines,  where  they  are  acted  on  by  the  pancreatic 
juice.  The  pancreas  secretes  a  proteolytic  enzyme, 
trypsin,  the  action  of  which  is  very  similar  to  that  of 
pepsin.  Unlike  pepsin,  it  is  destroyed  by  hydrochloric 
aei<l,  though  weak  organic  acids  do  not  prevent  its  action  ; 
it  acts  best  in  alkaline  solution,  the  optimum  degree  of 
alkalinity  being  that  of  \cfc  sodium  carbonate;  it  may 
act  in  neutral  solution.  It  possesses  the  power  of  split- 
ting a  portion  of  the  peptones  into  simpler  bodies, 
known  as  amido-acids,  such  as  leucin,  tyrosin,  and  as- 
partic  acid;  these  are  not  proteids.  Only  half  the 
peptones  formed  by  the  gastric  digestion  of  a  given 
quantity  of  proteid  can  be  converted  by  trypsin  into 
amido-acids.  Whether  the  peptones  formed  by  the 
action  of  pepsin  are  of  two  distinct  varieties  is  uncer- 
tain ;  it  has  been  supposed  that  albuminate  is  split  into 
two  forms  of  albumose,  called  hemi-albumose  and  anti- 
all  nunose,  and  that  these  are  converted  into  different 
forms  of  peptone;  in  the  one  case  hemipeptone,  in  the 
other,  antipeptone  ;  the  final  product  of  gastric  diges- 
tion being  a  mixture  of  these  two  peptones,  called 
ainphopeptones.  If  amphopeptoues  be  subjected  to  the 
action  of  trypsin,  the  hemipeptone  is  converted  into 
amido-acids,  leaving  antipeptone  unchanged.  This 
theory  is  known  as  the  cleavage  theory  of  proteid 
digestion.  Be  this  as  it  may,  it  is  perfectly  true 
that  more  than  one  form  of  albumose  appears  when 
pepsin  actvS  on  albumiuate.  Albuminate  is  split  up 


86  DIGESTION. 

into  proto-albumose  and  hetero-albumose,  but  as 
neither  of  these  can  be  converted  entirely  into  amido- 
acids,  neither  can  be  called  hemi-albumose  ;  neither  en- 
tirely resists  conversion  into  amido-acids,  so  neither  can 
be  pure  anti-albumose.  Both  proto-albumose  and 
hetero-albumose  are  changed  by  pepsin  into  deutero- 
albumoses,  which  differ  slightly  from  one  another  in 
solubility ;  these  are  converted  into  amphopeptones. 
Trypsin  converts  proteids  into  peptones  much  more 
rapidly  than  does  pepsin,  and  the  intermediate  products 
seem  to  be  less  numerous,  no  proto-albumose  and  no 
hetero-albumose  having  been  found  in  artificial  pancre- 
atic digestions.  The  albumin  is,  as  in  gastric  digestion, 
changed  to  albuminate,  this  time  alkali  albumin  ;  the 
albumiuate  is,  in  turn,  changed  to  deutero-albumoses, 
and  the  digestion  of  these  last  results  in  antipeptones 
and  amido-acids.  Possibly  the  deutero-albumoses  are 
split  directly  into  peptone  and  amido-acid  moieties ; 
this,  at  least,  is  the  simplest  way  of  expressing  the  re- 
sult. Pancreatic  juice  obtained  from  a  fasting  animal 
possesses  no  proteolytic  power. 

The  native  proteids,  albumins,  and  globulins  are  all 
digested  by  both  pepsin  and  trypsin,  and  pass  through 
the  same  stages ;  in  the  case  of  the  globulins,  the  third 
stage  is  that  of  globulose.  The  globuloses  may  be 
grouped  with  the  albumoses  under  the  head  of  pro- 
teoses.  The  solubility  of  these  different  proteids  is 
given  in  Table  1,  page  14. 

With  regard  to  the  amount  of  amido-acids  formed  in 
normal  intestinal  digestion,  observers  differ.  Accord- 
ing to  some,  very  little  leucin  or  tyrosin  appears,  the 
proteoses  and  peptones  being  absorbed  about  as  fast  as 
they  are  formed ;  according  to  others,  a  considerable 
percentage  of  the  peptones  is  normally  changed  to 
amido-acids. 


DIGESTION  OF  PROTEIDS.  87 

The  succus  entericus  contains  no  proteolytic  enzyme, 
ami,  consequently,  takes  no  part  in  the  digestion  of  pro- 
teids ;  its  enzymic  action  being  confined  to  that  which 
it  exercises  on  the  disaccharids  and  starch. 

There  are  present  in  the  intestine  bacteria  which 
cause  the  putrefaction  of  proteids  :  this  occurs  only  to 
a  slight  extent  in  the  small  intestine,  but  in  the  large  to 
a  considerable  degree.  As  long  as  carbohydrates  are 
present  the  action  of  bacteria  seems  to  be  exerted  on 
tin -i n  only,  the  proteids  being  spared.  The  nature  of 
this  bacterial  decomposition  of  proteids  is,  in  the  early 
stages,  very  similar  to  that  resulting  from  the  action  of 
pepsin  and  trypsin ;  there  are  formed  proteoses,  pep- 
tones, and  ty rosin.  In  addition,  however,  there  appear 
indol,  skatol,  phenol,  and  parakresol,  the  two  latter 
being  formed  from  ty  rosin ;  hydrogen  and  hydrogen 
snlphid  are  also  set  free.  The  indol,  skatol,  etc.,  are, 
liir  the  most  part,  excreted  with  the  feces,  and  are  an- 
swerable for  the  fecal  odor ;  to  a  certain  extent,  how- 
ever, they  are  absorbed,  and  carried  in  the  portal  blood 
to  the  liver.  These  substances  are  poisonous  if  admin- 
istered in  any  but  small  quantities.  The  amount 
absorbed  from  the  intestines  is  small,  and  exerts  no 
poisonous  action,  for,  in  the  liver,  a  chenlical  union 
between  each  of  these  substances  and  a  sulphate  is 
ln-o ught  about,  the  resulting  compound — for  example, 
potassiimi-phenyl-siilphate — being  harmless  ;  these  con- 
jugated sulphates  are  excreted  by  the  kidneys. 

The  pancreatic  digestion  of  proteids  seems  to  be 
favored  by  the  presence  of  bile;  at  least,  this  is  the 
ca-e  when  artificial  pancreatic  digestion  is  carried  on 
outside  the  body,  20  ^  more  peptones  being  formed  in 
a  given  time.  Bile  is  a  weak  antiseptic,  and  probably 
controls  to  a  certain  extent  the  growth  and  activity 
of  the  intestinal  bacteria.  It  would  appear  that  no 


88  DIGESTION. 

ptomains  are  formed  in  the  intestine,  though  bacteria 
capable  of  forming  them  are  present ;  were  they 
formed,  we  might  expect  ptomain  poisoning  to  follow 
every  proteid  meal.  Bacteria,  of  course,  enter  the 
stomach,  and,  as  has  been  stated,  bring  about  lactic 
acid  fermentation ;  as  soon,  however,  as  hydrochloric 
acid,  the  proteids  being  saturated,  appears  in  the  free 
state,  the  activity  of  bacteria  ceases.  The  hydrochloric 
acid  of  the  gastric  juice  also  aifords  a  certain  amount 
of  protection  against  pathogenic  bacteria ;  the  cholera 
bacillus  is  destroyed  by  it,  but,  unfortunately,  this  is 
not  the  case  with  the  tubercle  bacillus. 

The  native  proteids  are  not  all  digested  with  the 
same  ease ;  animal  proteids  are,  as  a  rule,  more  readily 
digested  than  those  found  in  vegetables.  An  indigesti= 
ble  residue  has,  nevertheless,  a  value,  for  without  it 
the  peristaltic  movements  of  the  intestines  are  not  so 
vigorous,  a  milk  diet  often  leading,  for  this  reason,  to 
constipation.  The  cellulose  of  vegetables  to  a  great 
extent  escapes  digestion,  and  affords  a  mechanical 
stimulus  to  the  intestinal  walls.  Proteids  which  have 
been  coagulated  by  cooking  are  less  readily  digested 
than  when  raw,  as  is  markedly  the  case  with  egg- 
albumen. 

Our  food  contains  considerable  quantities  of  nucleo= 
proteid,  and  this  during  gastric  or  pancreatic  digestion 
is  split  up  in  the  first  place  into  proteid  and  nuclein. 
The  proteid  moiety  is  digested  in  the  ordinary  manner 
and  converted  into  peptones,  etc.,  but  nuclein  is  almost 
indigestible ;  it  escapes  gastric  digestion  altogether,  is 
but  little  affected  by  the  pancreatic  juice,  and  is  for  the 
most  part  excreted  with  the  feces. 

Nucleo=albumins  differ  from  nucleoproteids  in  that 
they  are  compounds  of  proteid  with  pseudonuclein,  the 
latter  yielding,  on  decomposition,  no  xanthin  bases. 


DIGESTION  OF  PROTEIDS.  89 

The  most  familiar  nucleo-albumin  is  caseinogen,  the 
chief  nitrogenous  constituent  of  milk.  The  curdling 
of  milk  which  occurs  in  the  stomach  is  due  to  the 
coagulation  of  this  substance  by  the  rennin  of  gastric 
juice.  The  curdling  of  milk  which  occurs  outside  the 
body  is  due  to  the  precipitation  of  caseinogen  by  lactic 
acid,  formed  by  fermentation  of  milk-sugar;  the  curd 
thus  formed  differs  chemically  from  that  produced  by 
rcimiu.  Rennin  is  an  enzyme  which  acts  in  neutral, 
slightly  acid,  and  slightly  alkaline  solutions.  Under 
the  influence  of  rennin,  caseinogen  is  split  up,  probably 
through  hydrolysis,  into  soluble  casein,  and  whey  pro- 
teid which  is  also  soluble.  If  soluble  calcium  salts  be 
present,  the  soluble  casein  unites  with  calcium  to  form 
calcium  caseate,  which  is  insoluble  and  constitutes  the 
curd.  The  curd  then  contracts  and  expresses  the  whey, 
but  retains  the  fat  within  it.  The  whey  proteid  is 
readily  digested  by  either  pepsin  or  trypsin,  and  is  con- 
veiled  into  peptones.  The  first  step  in  the  digestion 
of  the  insoluble  casein,  calcium  caseate,  or  curd,  consists 
in  splitting  off  proteid,  the  pseudonuclein  remaining  as 
au  insoluble  precipitate.  The  proteid  thus  set  free  is 
digested  by  pepsin  and  hydrochloric  acid,  and  carried 
tli rough  the  proteose  stage  of  caseose,  iff  peptones. 
I  ><>iling  milk  renders  it  rather  less  readily  digestible  ;  in 
the  case  of  cow's  milk,  however,  this  effect  is  somewhat 
neutralized  by  the  fact  that  in  this  condition  it  curdles 
iu  small  flocculi  instead  of  in  large  masses,  so  that  it  is 
more  thoroughly  exposed  to  the  action  of  the  gastric 
jui<v.  In  this  respect  human  milk  behaves  like  boiled 
co\\'s  milk.  The  dilution  of  milk  accomplishes  the 
same  result. 

A  group  of  substances  known  as  albuminoids,  from 
tli-  fact  that  they  possess  many  of  the  characteristics  of 
albumin,  forms  another  important  division  of  food-stuffs ; 


90  DIGESTION. 

amongst  them  we  find  collagen  and  its  hydrate  gelatin, 
elastin,  keratin,  chondrin,  and  ossein,  the  two  latter 
being  impure  forms  of  collagen.  They  are  for  the  most 
part  less  readily  digested  than  proteids ;  keratin,  for  in- 
stance, being  altogether  indigestible.  Keratin  is  a  horny 
substance  found  in  hair  and  nails,  and  in  the  horny  layer 
of  the  epidermis.  Elastin  may  be  slowly  digested  by 
pepsin  or  trypsin,  the  resulting  products  being  elastoses 
resembling  the  proteoses.  Collagen  is  found  in  white 
fibrous  connective  tissue  and  in  bone  and  cartilage ;  it  is 
converted  by  boiling  or  by  the  action  of  the  gastric  juice 
into  gelatin.  Gelatin  is  insoluble  in  cold  water,  but  may 
be  readily  dissolved  in  hot ;  prolonged  boiling  destroys 
its  power  of  gelatinizing  on  cooling.  It  is  digested  by 
pepsin  or  trypsin,  and  converted  into  gelatoses  and  pep- 
tones ;  these  are,  however,  not  true  proteid  peptones. 
Although  the  percentage  composition  of  gelatin  very 
closely  resembles  that  of  proteid,  that  there  are  impor- 
tant differences  between  them  is  shown  by  the  fact  that 
gelatin  cannot  altogether  replace  the  proteids  of  our 
food,  though  it  can  better  do  so  than  either  fat  or  carbo- 
hydrate. Gelatin  cannot  be  built  up  into  the  proteid 
of  bioplasm,  it  is  simply  used  by  the  cell  as  fuel ;  it  can- 
not even  be  stored  up  as  collagen,  for  the  albuminoids 
of  the  body  are  all  formed  from  proteid. 

We  have  seen  that  proteids,  compound  proteids,  and 
some  of  the  albuminoids  are  during  digestion  converted 
into  proteoses  and  peptones,  which  may  be  absorbed ;  yet, 
if  introduced  into  the  circulation,  proteoses  and  peptones 
act  as  poisons,  producing  a  marked  fall  of  arterial  blood 
pressure,  and  narcosis ;  they  also  cause  a  temporary  loss 
of  coagulability  on  the  part  of  the  blood.  If  commercial 
peptones  be  injected  into  the  blood-vessels  of  a  dog  to  the 
extent  of  3^Vo  of  its  body-weight,  the  dose  proves  fatal. 
Yet  after  every  proteid  meal  these  poisonous  substances 


DIGESTION  OF  PROTEIDS.  91 

TABLE  4.— DIGESTION  OF  ALBUMINS  AND  GLOBULINS. 


- 
- 

5 

z 

1 

X 

Native  protcid 

"•% 

ate 

s 

b. 

—  *. 
jteosei 
—  *-„— 

b. 

A  

'epton 

•*- 

.  b. 

•  ..  s. 

Gastric  epi- 
thelium 

•SP 

blood 

a.         b 

'"i 

• 
^ 
\ 
/• 
M 

C 

\\'''.\\ 

r 
m 

- 

;•, 

•_ 

'r 

/« 

f 
1 

f  native  ) 
{  proteid  }" 

f  native  ) 

- 

s 

es 

—  \ 

\  proteid  / 

« 

i 
^— 
Albi 

/   - 

a. 

4 

i- 

- 

Mi 

- 
^ 

• 

j 
ID 

- 

• 

to* 

•^ 
'     - 

«^ 

Intestinal 
epithelium 

blood 

f  native  ) 
{  proteid  ]•  - 

X 

- 

• 

N 

s»—  • 

b.  

c. 
t 

H 

Peptones.  J 
lb. 

Amido- 
acids 

a.            b.  ->• 

f  native  ) 
1  proteid  /  — 

i        i 

Indol,  Ski 

ttol,  Phenol,  etc. 

/— 

a. 

-^—  s 

eces. 
t 

•  •  •  (small  quantity) 

92  DIGESTION, 

are  absorbed  in  quantity  by  the  epithelial  cells  which 
line  the  intestines.  Peptones  are,  however,  not  found 
in  the  blood  under  ordinary  circumstances,  and  if  they 
reach  the  blood,  are  at  once  excreted  (provided  the 
blood  pressure  is  not  too  much  depressed)  by  the  kid- 
neys. It  appears  that  the  epithelial  cells,  having  taken 
up  the  peptones,  reconvert  them  by  synthesis  into  native 
proteids,  and  discharge  them  in  this  condition  into  the 
lymph,  from  which  they  pass  into  the  blood-capillaries. 
The  work  done  by  the  digestive  juices  might,  at  first 
sight,  appear  to  be  labor  spent  in  vain,  for  the  peptones 
so  formed  must  be  reconverted  into  albumins  or  globulins 
by  the  epithelial  cells,  and  this  entails  the  expenditure 
of  a  large  amount  of  energy ;  further,  it  has  been  shown 
that  soluble  native  proteids  may  be  absorbed  without 
undergoing  digestion.  We  must,  however,  remember 
that  peptones  are  more  readily  absorbed  than  undigested 
proteids,  and  that  coagulated  proteids  are  incapable  of 
absorption  until  they  have  been  rendered  soluble  by  di- 
gestion. Again,  gelatin,  egg-albumen,  casein,  and  sev- 
eral other  forms  of  soluble  proteids  are  nonassimilable, 
and  if  injected  directly  into  the  circulation  are  excreted 
by  the  kidneys.  These  substances  must  undergo  some 
change  in  constitution  before  they  can  be  utilized  as  food 
by  the  cells  of  the  body.  The  epithelial  cells  which  line 
the  intestines  evidently  possess  the  power  of  bringing 
about  this  rearrangement  of  the  molecule  of  egg-albumen, 
provided  it  has  not  been  rendered  insoluble  by  cooking, 
but  it  is  possible  that  the  change  is  more  readily  effected 
after  digestion  has  occurred ;  it  may  be  easier  for  the 
epithelial  cell  to  construct  serum  albumin  out  of  egg- 
albumen  peptones  than  out  of  the  native  unchanged 
egg-albumen. 

The  gastric  digestion  of  proteids  is,  on  the  whole, 
favored  by  the  use  of  small  quantities  of  alcohol.     It  is 


DIGESTION  OF  FAT.  93 

true  that  the  presence  of  alcohol  somewhat  retards  the 
action  <>t'  pepsin,  but  alcohol  taken  in  small  quantities  is 
rapidly  absorbed  from  the  stomach.  It  stimulates  the 
gastric  glands  to  more  rapid  secretion  of  the  gastric 
juice,  and  in  this  way,  at  least  in  cases  where  the  pro- 
cess is  less  active  than  normal,  hastens  digestion. 

Not  all  the  proteid  of  the  food  is  digested  and  ab- 
sorbed; a  variable  amount,  especially  of  the  vegetable 
proteid,  is  excreted  with  the  feces. 

Digestion  of  Fat.  —  Fats  are  digested  neither  in  the 
mouth  nor  in  the  stomach,  but  in  the  latter  may,  to  a 
HI  mil  extent,  undergo  bacterial  decomposition.  In  the 
intestine  they  are  emulsified.  Fats  which  contain  some 
live  fatty  acid  may  be  emulsified  by  the  soap  which  is 
formed  by  the  union  of  this  fatty  acid  with  sodium,  the 
latter  being  derived  from  the  sodium  carbonate  of  the 
pancreatic  juice  and  bile.  Neutral  fats,  which  contain 
no  tree  fatty  acid,  are  also  emulsified  in  the  intestine,  but 
not  quite  so  readily,  for  in  this  case,  before  emulsification 
can  take  place,  some  of  the  fat  must  be  split  up  with  the 
liberation  of  fatty  acid,  which,  with  sodium,  forms  soap. 
The  splitting  of  the  fat  is  caused  by  an  enzyme  of  the 
pancreatic  juice,  called  steapsin,  or  pialyn.  The  change 
produced  is  hydrolytic,  one  molecule  of  fait  being  hy- 
dra ted  and  split  up  with  the  formation  of  one  molecule 
of  glycerin  and  three  molecules  of  fatty  acid  ;  for 
example  : 


C3H5(C18H3502)3  +  3H,0  =  CjHjCOH),  +  3C17H?5CO2H. 
Stearin  Glycerin  Stearic  Acid 

It  is  probable  that  all  the  fat  which  is  absorbed  is 
first  split  up  in  this  way  ;  some  of  the  fatty  acid  set  free 
is  combined  as  soap,  and  by  emulsifying  the  rest  of  the 
fat,  hastens  its  digestion,  for  in  this  way  the  fat  is  more 
completely  exposed  to  the  action  of  the  steapsin  ;  an- 


94 


DIGESTION. 


other  portion  is  probably  absorbed  by  the  epithelium  as 
fatty  acid.  Fatty  acids  are  insoluble  in  water,  but  in 
the  intestine  they  are  held  in  solution  by  the  presence 
of  bile  salts,  sodium  glycocholate  and  sodium  tauro- 
cholate :  the  favorable  influence  exerted  by  bile  on  the 
digestion  of  fat  probably  depends  on  this  property. 
Some  of  the  fatty  acid  may  be  absorbed  as  soap.  It 
is  highly  improbable  that  fat  is  absorbed  without  under- 
going digestion,  as  has  been  supposed.  The  fatty  acid 
which  is  absorbed  is,  by  the  epithelial  cells,  recombined 
with  glycerin  to  form  fat ;  the  absorbed  soap  is  combined 
in  the  same  way,  the  sodium  being  first  split  off  and 
united  with  some  other  acid  radicle.  Even  if  fatty  acid 
be  administered  in  the  absence  of  glycerin,  it  may  be 
converted  into  fat  in  the  epithelial  cells,  which  in  this 
case  appear  to  manufacture  the  glycerin.  In  the  absence 
of  bile,  the  absorption  of  fat  is  defective,  much  of  it 
undergoing  bacterial  decomposition  into  fatty  acids  in 
the  large  intestine  and  being  excreted  in  the  feces. 

TABLE  5.— DIGESTION  OF  FAT  IN  THE  INTESTINE. 


Fat 


Glycerin- 


Fatty  acid  -> 


.  +  Na2C03= 


Soapi- 


H20  +  C02 


Intestinal 
epithelium 


Fat  — 


Lymph 


The  fat  which  passes  from  the  intestinal  epithelial 
cells  into  the  lymph-spaces  of  the  villi  does  not  enter 

1  The  soap  first  formed  causes  the  emulsification  of  the  remain- 
ing fat. 


BILE.  95 

the  blood-capillaries,  but  passes  through  the  lymphatic 
vessels  into  the  thoracic  duct,  and  so  reaches  the  subcla- 
vian  vein,  where  it  is  mixed  with  the  blood.  The  solu- 
ble constituents  of  the  food,  on  the  other  hand,  pass 
from  the  lymph-spaces  of  the  villi  into  the  blood-capil- 
laries, for  the  percentage  of  sugar  and  proteids  in  the 
lymph  which  reaches  the  thoracic  duct  is  very  little  in- 
creased during  absorption.  Sugars  and  proteids  may 
be  absorbed  in  the  stomach  to  a  certain  extent,  but  in 
the  intestine  conditions  are  much  more  favorable  to  ab- 
sorption. Water  is  not  absorbed  from  the  stomach,  but 
passes  on  into  the  intestines  ;  it  is  absorbed  most  rapidly 
in  the  ileum  aud  large  intestine. 

Bile. — The  chief  constituents  of  bile,  as  secreted  by 
the  liver,  are  water,  bile  salts,  inorganic  salts,  pigments, 
cholesterin,  lecithin,  and  soaps.  To  these,  as  the  bile 
passes  through  the  ducts,  and  during  its  stay  within  the 
gall-bladder,  is  added  mucin.  The  bile  salts  are  sodium 
glycocholate  and  sodium  taurocholate;  in  human  bile 
the  former  predominates.  They  are  present  in  bile  to 
the  extent  of  about  7.5  c/0 .  They  are  largely  reabsorbed, 
but  in  the  intestine  a  portion  of  these  salts  may  be 
hydrolyzed  through  the  action  of  bacteria,  as  follows : 

C2«H4306    -f     H20    =    C24H4005     +    CH2.NH2.C02H 

(ilyL-ucholic  Acid  Cholic  Acid  Glycocol 

C26H4306    +    H.,0    =    C24H4005    +    C2H4NH2S02OH 

Tanrocholic  Acid  Cholic  Acid  Taurin 

The  taurin,  glycocol,  and  part  of  the  cholic  acid  formed 
'  are  absorbed.  The  bile  salts  are  useful  in  holding  in 
solution  cholesterin  and  lecithin,  and  appear  to  be  used 
more  than  once,  possibly  over  aud  over  again.  It  has 
already  been  mentioned  that  they  exert  an  important 
influence  on  the  absorption  of  fat.  The  bile  pigments, 
bilirubiu  and  biliverdiu,  originate  from  the  hemoglobin, 


96  DIGESTION. 


:: 


of  broken-down  red  blood-cells  ;  they  contain,  howeve 
no  iron,  this  being  split  off  and  retained  in  the  liver, 
where    the   bile   pigments    are  formed.     The  iron   so  | 
retained  may  be  used  in  the  synthesis  of  new  hemo- 
globin.    A  certain  amount  of  bile  pigment  seems  to  be 
reabsorbed    from  the  intestine,  to  be  again  excreted. 
Most  of  the  pigment  is  reduced  by  the  action  of  the 
free  hydrogen  in  the  intestine,  or,  through  putrefaction, 
to   hydrobilirubin,    some   of    which    is   absorbed   and  I 
eliminated  by  the  kidneys ;    in  the  urine  it  is  called  | 
urobilin. 

Movements  Concerned  in  Digestion. — Secretion 
of  the  Digestive  Juices. — Mastication  is  performed 
by  movements  of  the  lower  jaw,  the  muscles  concerned 
being  innervated  through  the  inferior  maxillary  brand: 
of  the  fifth  cranial  nerve.  The  food  is  kept  betweer 
the  teeth  by  movements  of  the  tongue  and  contractior 
of  the  muscles  of  the  cheeks.  The  food  is  thus  no1 
only  ground  up,  but  is  mixed  with  the  saliva.  Tl 
latter  is  secreted  by  three  pairs  of  glands,  the  parotid 
submaxillary,  and  sublingual  glands ;  and  to  a  smalle 
extent  by  the  glands  of  the  oral  mucous  membrane 
The  activity  of  the  salivary  glands  is  controlled  by  the 
central  nervous  system,  the  salivary  centers  bein 
situated  in  the  spinal  bulb.  Two  sets  of  secreto 
nerves,  cranial  and  sympathetic,  are  distributed  to  eac 
gland.  The  cranial  nerve-fibers  (pre-ganglionic)  whic 
innervate  the  parotid  leave  the  bulb  in  the  ninth  craui 
nerve  and  probably  end  in  the  otic  ganglion  in  contact 
relations  with  nerve-cells  whose  axons  (post-ganglionic) 
reach  the  parotid  through  the  auriculotemporal  branch 
of  the  trifacial.  The  cranial  fibers  which  control  the  ] 
submaxillary  and  sublingual  glands  emerge  from  the 
bulb  in  the  facial  nerve,  and,  by  way  of  the  chorda 
tympani,  reach  the  submaxillary  and  sublingual  ganglia. 


MOVEMENTS  CONCERNED  IN  DIGESTION.  97 

In  these  ganglia  they  end,  and  make  physiologic  con- 
in  ct  ion  with  cells  whose  post-gangl ionic  fibers  are  dis- 
tributed to  the  gland-cells.  Post-ganglionic  sympathetic 
nerve-fibers  from  the  superior  cervical  sympathetic 
ganglion  are  supplied  to  each  of  these  glands.  The 
cranial  secretory  fibers  are  accompanied  by  vasodilator 
fibers  ;  the  sympathetic,  by  vasoconstrictors. 

Artificial  stimulation  of  the  chorda  tympani  produces 
a  result  which  differs  widely  from  the  effect  of  stimula- 
ting the  cervical  sympathetic.  In  the  former  case,  the 
submaxillary  gland  secretes  abundant  watery  saliva ; 
in  the  latter  case,  the  secretion  is  thick  and  scanty. 
Stimulation  of  the  chorda  tympani  of  course  increases 
the  blood  supply  of  the  gland,  and  thus  renders  a 
copious  secretion  possible,  but  the  variation  of  the 
1)1  ood  supply  probably  does  not  account  altogether  for 
the  difference  in  the  two  results.  The  normal  secretion 
of  saliva  is  a  reflex  event.  It  is  readily  initiated  by 
stimulation  of  the  terminations  of  the  afferent  nerves 
of  the  oral  mucous  membrane  by  food  or  other  sub- 
stances placed  in  the  mouth,  weak  acids  forming  a 
particularly  effective  stimulus.  Reflex  secretion  of 
saliva  is  not  brought  about  through  the  sympathetic 
nerve-fibers,  but  only  through  the  cranial  fibers.  The 
si li vary  centers  are  not  under  the  control  of  the  will, 
but  by  thinking  of  food  we  may  cause  the  dispatch  of 
involuntary  nerve  impulses  from  the  brain  to  the 
salivary  centers,  and  thus  indirectly  bring  about  a  flow 
of  saliva.  These  centers  may  be  not  only  excited 
through  the  emotions,  as  by  the  sight  or  smell  of  food, 
but  they  may  also  be  inhibited,  as  by  fear  or  nervous 
worry.  Reflex  secretion  of  saliva  may  result  from 
simulation  of  afferent  nerves  in  parts  of  the  body  other 
than  the  mouth;  irritation  of  the  gastric  mucous 
membrane  may  cause  it,  a  flow  of  saliva  usually  pre- 

7 


98  DIGESTION 

ceding  vomiting.  Irritation  of  the  uterus  may  also  be 
effective,  the  early  stages  of  pregnancy  often  being 
accompanied  by  profuse  secretion  of  saliva.  After 
division  of  the  chorda  tympani  there  follows  a  slow 
continuous  secretion  of  saliva  by  the  submaxillary 
gland ;  this  is  called  paralytic  secretion,  and  probably 
results  from  a  local  stimulation  of  the  group  of  nerve- 
cells  in  the  gland  which  form  the  submaxillary  ganglion. 
How  the  stimulus  originates  is  unknown,  and  it  may  be 
that  the  activity  of  the  nerve-cells  is  increased  by  the 
cessation  of  inhibitory  impulses,  which  normally  are 
perhaps  transmitted  to  them  through  the  chorda 
tympani.  The  administration  of  atropin  causes  dry  ness 
of  the  mouth,  by  paralyzing  the  terminations  of  the 
post-ganglionic  fibers  of  the  cranial  nerve  supply ;  the 
sympathetic  fibers  are  not  affected.  Pilocarpin  provokes 
secretion,  apparently  by  stimulating  the  terminations  of 
the  same  fibers. 

The  food,  after  being  masticated  and  mixed  with  the 
saliva,  is  swallowed.  Only  the  first  of  the  movements 
which  play  a  part  in  deglutition  are  voluntary.  If  the 
mouth  be  empty  of  anything  that  could  be  swallowed, 
including  saliva,  it  is  impossible  to  voluntarily  provoke 
all  the  swallowing  movements.  They  are  for  the  most 
part  purely  reflex,  and  are  excited  through  the  afferent 
nerves  of  the  soft  palate,  of  the  back  of  the  tongue, 
and  of  the  fauces,  which  are  stimulated  by  the  contact 
of  food,  or  any  other  substance,  with  the  mucous 
membrane  covering  these  parts.  The  first  part  of  the 
action,  which  may  be  accomplished  voluntarily,  con- 
sists in  the  approximation  of  the  tip  of  the  tongue  to 
the  hard  palate,  followed  by  a  raising  of  the  floor  of 
the  mouth  and  tongue  by  the  contraction  of  the  mylo- 
hyoid  muscles.  This  forces  the  food  back  through  the 
fauces  into  the  pharynx  ;  in  the  case  of  liquid  no  further 


MOVEMENTS  CONCERNED  IN  DIGESTION.  99 

muscular  action  is  necessary  to  carry  it  as  far  as  the 
lower  end  of  the  esophagus;  nevertheless,  the  contrac- 
tion of  several  muscles,  in  regular  sequence,  follows. 
As  the  food  enters  the  pharynx,  it  is  prevented  from 
passing  upward  into  the  nasal  pharynx  by  the  contrac- 
tion of  the  levatores  palati  and  superior  constrictors  of 
the  pharynx,  which  occurs  even  before  the  food  touches 
the  soft  palate  ;  its  entrance  into  the  larynx  is  prevented 
I ><it  h  by  the  contraction  of  the  arytenoid  muscle,  which 
pulls  the  posterior  border  of  the  opening  of  the  larynx 
forward,  and  by  the  thyrohyoid  muscles,  which  raise 
the  larynx.  At  the  same  time  the  glottis  is  closed,  and 
the  respiratory  center  inhibited  through  the  glosso- 
pharyngeal  nerve.  The  downward  passage  of  solid 
i<  x  x  I  is  furthered  by  the  contraction  of  the  constrictors 
of  the  pharynx  and  the  esophageal  muscles;  these  also 
contract  on  the  deglutition  of  liquid,  though  their 
assistance  seems  to  be  unnecessary.  If  successive 
mouthfuls  of  liquid  be  swallowed,  the  esophageal  mus- 
cle-; and  cardiac  sphincter  are  inhibited  and  remain  lax. 
Th«'  center  (or  centers)  controlling  deglutition  is  situated 
in  the  spinal  bulb  ;  the  afferent  nerves  concerned  in  the 
retlex  are  the  fifth  and  ninth  cranial  nerves  and  the 
superior  laryngeal  branch  of  the  tenth;  tne  artificial 
simulation  of  this  latter  nerve  may  cause  swallowing 
movements  when  the  pharynx  is  empty. 

The  entrance  of  food  into  the  stomach  is  followed  by 
secretion  of  gastric  juice,  flushing  of  the  mucous  mem- 
brane, and  muscular  movements  of  the  stomach-wall. 
These  events  may  also  be  induced  by  the  taking  of  food 
into  the  mouth,  or  even  by  the  sight  of  food.  The 
efferent  nerve  concerned  in  the  reflex  secretion  of  gastric 
juice  is  the  vagus,  but  after  division  of  both  vagi,  secre- 
tion still  occurs  on  the  introduction  of  food  into  the 
stomach  ;  in  this  case  it  may  be  controlled  by  nerve-cells 


100  DIGESTION. 

situated  in  the  walls  of  the  stomach  itself.  The  effect 
produced  by  the  introduction  of  food  varies  considerably 
with  the  nature  of  the  food ;  mere  mechanical  stimulation 
causes  but  a  scanty  secretion,  while  peptones  are  particu- 
larly effective  ;  they  perhaps  stimulate  the  gland  cells  or 
local  nerve-cells  after  absorption.  The  vagus  also  con- 
tains visceroniotor  nerve-fibers  for  the  stomach ;  the 
sympathetic  may  supply  a  few  motor  fibers,  but  the 
usual  effect  of  stimulating  this  nerve  is  the  inhibition  of 
gastric  movements.  After  division  of  all  the  nerves  re- 
ceived by  the  stomach,  and  even  after  its  removal  from 
the  body,  its  contractions  may  continue  in  normal  se- 
quence ;  this  must  be  due  either  to  the  action  of  a  local 
nervous  mechanism,  or  to  the  nature  of  the  muscle 
itself.  The  movements  which  occur  on  the  introduction 
of  food  are  at  first  feeble,  but  increase  in  force  as 
digestion  proceeds.  The  contractions  of  the  pyloric  end 
are  the  more  marked,  and  are  peristaltic ;  the  contrac- 
tions of  the  cardiac  end,  or  fundus,  being  tonic.  The 
peristaltic  movements  of  the  pyloric  end,  or  antruni, 
serve  to  keep  the  food  in  motion,  and  to  press  the  already 
digested  portion  through  the  pylorus,  which  relaxes  at 
intervals.  The  vagus  also  transmits  to  the  stomach  in- 
hibitory nerve-fibers ;  it  is  perhaps  through  these  that 
its  movements  are  lessened  by  disagreeable  emotions. 
The  entrance  of  food  into  the  stomach  provokes  not  only 
a  reflex  secretion  of  gastric  juice,  but  of  pancreatic  juice 
also,  the  efferent  secretory  nerve  being  in  each  case  the 
vagus.  Therefore  when  the  first  portion  of  the  chyme 
passes  into  the  duodenum,  pancreatic  juice  will  have 
begun  to  accumulate  here.  The  secretion  of  bile  is  also 
hastened  by  the  introduction  of  food  into  the  stomach, 
but  this  accumulates  in  the  gall-bladder,  and  does  not 
enter  the  duodenum  until  a  reflex  contraction  of  the 
gall-bladder  is  instituted  by  the  stimulation  of  the  duo- 


MOVEMENTS  CONCERN  Kl>  'X  Dl£fcSTIX>K  '/' '  101 

denal  mucous  membrane  caused  by  the  acid  chyme. 
The  rhyme  then  will  be  mixed  with,  and  neutralized  by, 
the  alkaline  bile  and  pancreatic  juice;  the  pepsin  will 
be  rapidly  destroyed  by  the  trypsin  and  sodium  car- 
Inmate,  and  the  partly  digested  proteids  precipitated  by 
the  bile  salts.  The  secretion  of  pancreatic  juice  is  not 
entirely  dependent  on  the  central  nervous  system  ;  there 
exist  local  ganglia  which  govern  the  activity  of  this 
gland.  The  secretion  of  bile  seems  to  be  influenced 
im  >re  or  less  by  the  absorbed  products  of  gastric  digestion. 
I  )uring  starvation  the  intestines  are  pale  and  motionless, 
l)i it  after  the  taking  of  food  they  become  flushed  with 
blood  and  exhibit  movements  of  two  kinds,  rhythmic 
and  peristaltic.  The  rhythmic  or  pendular  movement 
(••insists  of  a  swaying  of  the  intestinal  loops  occasioned 
by  the  contraction  of  both  the  longitudinal  and  circular 
nials  of  muscle,  constriction  being  but  little  in  evidence. 
The  wave  of  contraction  passes  over  the  intestines,  from 
above  downward,  from  twenty  to  fifty  times  as  rapidly 
as  the  peristaltic  contractions.  The  rhythmic  move- 
ments are  of  muscular,  the  peristaltic  of  nervous,  origin. 
As  in  the  case  of  the  stomach,  the  vagus  supplies  the 
intestine  with  both  motor  and  inhibitory  nerve-fibers ; 
tin  sympathetic  supplies  chiefly  inhibitor}7  fibers.  These 
nerves  appear,  however,  to  exert  only  a  regulatory  influ- 
ence over  the  intestinal  movements,  for  after  the  division 
of  all  the  extrinsic  nerves,  peristalsis  may  continue  or  he- 
mine  exaggerated  ;  the  nerve-cells  of  Auerbach's  plexus 
pn  >1  >ablv  constitute  a  local  mechanism  by  which  peristalsis 
is  <•(  tordinated.  The  movement  consists  of  a  constriction 
which  travels  from  the  duodenum  downward  at  the  rate 
of  alxwt  1  mm.  per  second,  and  is  preceded  by  a  wave 
of  relaxation  ;  the  latter,  of  course,  increases  the  ease 
with  which  the  contents  of  the  intestine  are  pressed 
onward  by  the  constriction  following  in  its  wake.  If  a 


K)2  .DIGESTION. 

local  stimulus  be  applied  to  the  mucous  membrane  of 
the  intestine,  a  constriction  appears  above  the  point 
stimulated,  while  for  some  distance  below,  the  muscles 
are  inhibited  and  relax. 

The  large  intestine  shows  similar  peristaltic  move- 
ments, which  begin  at  the  ileocecal  valve,  and  are  prop- 
agated in  the  direction  of  the  rectum,  but  do  not  reach 
it.  The  feces  accumulate  in  the  sigmoid  flexure.  The 
descending  colon,  rectum,  and  anus  receive  two  sets  of 
nerve-fibers,  one,  coming  through  the  sympathetic,  from 
the  lumbar  region  of  the  cord  (the  pre-ganglionic  fibers 
ending  in  the  inferior  mesenteric  ganglia),  the  other, 
from  the  sacral  portion  of  the  cord  through  the  nervi 
erigentes,  the  pre-ganglionic  fibers  of  this  set  ending  in 
small  ganglia  near  the  part  innervated.  The  first  set 
are  for  the  most  part  motor,  the  latter  inhibitory. 
Ordinarily  the  rectum  is  empty,  and  is  only  thrown  into 
reflex  peristalsis  by  the  entrance  of  feces  from  above  ; 
defecation  may  be  delayed  by  the  contraction  of  the 
internal  and  external  sphincters  of  the  anus,  the  former 
consisting  of  involuntary,  the  latter  of  voluntary,  mus- 
cle. The  filling  of  the  rectum  gives  rise  to  a  desire 
to  defecate,  which  may  or  may  not  be  resisted ;  if  the 
former,  the  contraction  of  the  external  sphincter  is 
voluntarily  strengthened  ;  if  the  latter,  the  emptying  of 
the  rectum  is  assisted  by  a  contraction  of  the  abdominal 
muscles  and  inhibition  of  the  external  sphincter,  the 
internal  sphincter  being  at  the  same  time  reflexly  inhib- 
ited. If  by  injury  to  the  spinal  cord  voluntary  nerve 
impulses  are  prevented  from  reaching  the  centers  in  the 
lumbar  region,  defecation  becomes  purely  reflex,  and 
may  be  carried  on  without  the  aid  of  the  will.  If  the 
lumbar  portion  of  the  cord  be  destroyed,  the  reflex 
mechanism  is  put  out  of  existence,  and  fecal  inconti- 
nence results. 


QUESTIONS.  103 

Vomiting  is  a  reflex  action  which  usually  results 
from  irritation  of  the  gastric  mucous  membrane,  and  is 
preceded  by  a  feeling  of  nausea.  It  may  also  be 
excited  in  a  variety  of  other  ways  ;  for  instance,  mechan- 
ical irritation  of  the  pharynx,  intestinal  obstruction, 
irritation  of  the  uterus,  as  in  pregnancy,  and  through 
the  emotions.  It  is  brought  about  mainly  by  strong 
contractions  of  the  diaphragm  and  abdominal  muscles, 
with  simultaneous  closure  of  the  glottis.  The  stomach 
is  thus  compressed  and  its  contents  ejected  through  the 
esophagus,  the  cardiac  sphincter  being  meantime  relaxed. 
1  he  walls  of  the  stomach  take  some  part  in  the  expul- 
sion of  the  food,  but  unassisted  are  ineffective.  Vomit- 
ing is  controlled  by  a  center  situated  in  the  medulla. 


QUESTIONS  FOR  CHAPTER  IV. 

What  foods  actually  require  digestion  before  they  can  be  ab- 
sorbed? 

Does  proteid  undergo  any  preparation  for  absorption  in  the 
month? 

If  raw  starch  and  saliva  be  mixed,  will  the  digestion  of  the 
former  be  assisted  by  boiling  the  mixture? 

If  starch  paste  be  acidified  with  HC1,  the  addition  of  what  sub- 
stance will  enable  saliva  to  digest  the  starch? 

If  starch  and  saliva  be  mixed,  and  a  drop  of  the  mixture  be 
ti->trd  at  intervals  with  iodin  solution,  why  does  the  color  reaction 
vary? 

What  step  in  digestion  which  is  of  more  importance  than  the 
salivary  digestion  of  starch  is  carried  on  in  the  mouth? 

Why  is  it  well  to  wash  the  teeth  after  each  meal  ? 

What  secretion  possesses  the  widest  range  of  digestive  power? 

Can  you  readily  arrange  the  digestive  secretions  in  the  order  of 
their  relative  importance  ? 

How  is  digestion  affected  by  removal  of  the  stomach  ? 

In  what  respect  is  digestion  most  interfered  with  by  removal 
of  the  pancreas  ? 


104  DIGESTION. 

Which  of  the  following  substances  are  of  equal  value  as  food, 
whether  they  be  injected  directly  into  the  blood  stream  or  intro- 
duced into  the  alimentary  canal :  dextrose,  cane-sugar,  soluble 
starch,  lactose,  egg-albumen,  peptones,  raw  serum  albumin,  cooked 
serum  albumin,  levulose  ? 

Supposing  that  pyloric  and  duodenal  fistulse  have  been  estab- 
lished, so  that  there  is  no  communication  between  the  stomach  and 
intestines,  the  animal  may  be  fed  through  the  mouth,  or  by  intro- 
ducing food  and  water  directly  into  the  duodenum.  Which  method 
of  feeding  will  prove  the  more  satisfactory  ? 

What  effect  on  digestion  has  the  existence  of  a  biliary  fistula? 

How  does  fat  reach  the  blood  stream  ? 

How  is  digestion  modified  by  the  absence  of  hydrochloric  acid 
from  the  gastric  juice  ? 

What  constituents  of  food  require  no  digestion  ? 

What  different  factors  play  a  part  in  determining  the  reaction 
of  the  intestinal  contents? 

If  a  small  quantity  of  egg-albumen  be  absorbed  from  the  intes- 
tines without  having  undergone  digestion,  how  is  it  that  it  does 
not  appear  in  the  urine  ? 

Under  what  circumstances  does  glycerin  appear  in  the  intes- 
tines? 

How  does  dextrin  differ  from  starch  in  its  physical  properties? 

Where  and  how  is  bread  and  butter  digested  ? 

Why  is  it  impossible  to  swallow  six  times  in  rapid  succession 
without  placing  something  in  the  mouth  ? 

Have  the  emotions  any  influence  over  digestion  ?  and  is  the  effect 
of  all  emotions  the  same  ? 

Why  should  the  addition  of  horn  shavings,  which  are  indigest- 
ible, enable  a  rabbit  to  live  on  a  milk  diet  ? 

How  is  it  that  proteid  food  does  not  result  in  peptone  poison- 
ing? 

What  becomes  of  the  hemoglobin  of  the  red  cells  which  break 
down? 

If  soluble  starch  is  absorbed  from  the  intestine,  why  does  it  not 
appear  in  the  blood  ? 

What  evidence  of  constipation  may  be  shown  by  the  urine? 

What  instances  of  synthesis  in  the  body  can  you  mention  ? 


CHAPTER  V. 

METABOLISM  AND  NUTRITION* 

THE  food,  after  digestion  and  absorption,  reaches  the 
lymph-spaces  of  the  gastric  and  intestinal  mucous  mem- 
hranes.  The  proteids  and  carbohydrates  pass,  for  the 
niitst  part,  from  the  lymph  into  the  blood-capillaries, 
and  are  carried  through  the  portal  vessels  to  the  liver ; 
tin-  flit,  on  the  other  hand,  reaches  the  subclavian  vein 
through  the  lymphatic  vessels.  During  the  absorption 
of  fat,  the  lymph  which  passes  through  the  lymphatic 
vessels  of  the  mesentery,  or  lacteals,  resembles  milk  in 
appearance,  and  is  called  chyle. 

As  we  have  seen,  the  carbohydrates  reach  the  blood 
ehiefly  in  the  form  of  dextrose.  If  during  absorption 
samples  of  blood  be  taken  from  the  portal  and  hepatic 
veins  and  compared,  it  will  be  found  that  the  hepatic 
Mood  contains  the  smaller  percentage  of  sugar.  Evi- 
dently, then,  during  absorption  sugar  disappears  from 
the  blood  as  it  passes  through  the  liver.  If  the  liver  of 
a  well-fed  animal  be  examined  with  the  microscope,  the 
liver-cells  will  be  seen  to  contain  an  opalescent  sub- 
stance, which  lies  in  that  portion  of  the  cell  adjacent  to 
the  blood-capillary.  On  treatment  with  iodin,  this  sub- 
stance gives  a  port-wine  color  reaction,  resembling  that 
niven  with  iodin  by  erythrodextrin.  It  is  a  carbohy- 
drate with  the  formula  (CrH10O5)n,  the  molecule  being 
smaller  than  that  of  starch  ;  according  to  observations 
made  on  the  freezing-point  of  its  solutions,  it  may  be 
represented  as  (C6H10O5)10.  Like  starch,  glycogen  is 

105 


106  METABOLISM  AND  NUTRITION. 

nondialyzable  ;  unlike  starch,  it  is  readily  soluble.  On 
starvation,  glycogen  rapidly  disappears  from  the  liver. 
If  through  the  vessels  of  an  excised,  glycogen-free  liver 
there  be  kept  up  an  artificial  flow  of  blood  which  con- 
tains dextrose,  the  percentage  of  sugar  in  the  blood 
diminishes,  and  glycogen  appears  in  the  liver-cells.  The 
conversion  of  sugar  into  glycogeu  is  synthetic,  and  con- 
sists in  the  following  reaction  : 


10C6H1206  =  (C6H1005)10  +  10H20; 
Dextrose  Glycogeu 


that  is,  if  we  may  take  the  above  formula  to  represent 
glycogen.  Not  all  the  sugar  which  reaches  the  liver  is 
converted  into  glycogen ;  a  large  proportion  passes 
through  the  liver  unchanged  and  is  distributed,  through 
the  arteries,  to  the  system  in  general.  Sugar  is  rapidly 
taken  up  from  the  lymph  by  the  muscles ;  a  certain 
amount  being  converted  by  them  into  and  stored  as  gly- 
cogeu. Taken  collectively,  the  muscles  may  contain  as 
much  glycogen  as  is  found  in  the  liver,  but  in  muscle 
the  percentage  is  smaller.  Some  of  the  sugar  taken  up 
by  the  muscles  may  perhaps  at  once,  without  undergoing 
previous  elaboration,  be  utilized  as  a  source  of  energy, 
being  burnt  up  with  the  formation  of  carbon  dioxid  and 
water ;  it  is  probable,  however,  that  an  active  muscle 
which  uses  an  excess  of  sugar  does  not  carry  the  oxida- 
tion of  this  excess  beyond  the  formation  of  lactic  acid, 
C3H6O3,  and  that  this  lactic  acid  is  completely  oxidized 
elsewhere.  Exercise  reduces  the  amount  of  glycogen 
held  in  muscle,  but  that  other  substances  may  afford  a 
supply  of  energy  for  muscular  work  is  shown  by  the 
fact  that  a  muscle  may  perform  work  after  all  its  glyco- 
gen has  disappeared.  If  a  muscle  is  paralyzed  by  divi- 
sion of  its  nerve  supply,  an  accumulation  of  glycogen 
goes  on  within  it  for  several  days.  Other  portions  of 


GLYCOSURIA.  107 

the  sugar  received  by  a  muscle  may,  within  it,  be  com- 
bined with  some  other  substance, — for  instance,  proteid, 
— or  it  may  be  con  verted  into  and  stored  as  fat.  During 
starvation,  when  all  the  glycogen  has  disappeared  from 
the  liver  and  muscles,  and  when  the  body's  store  of  fat 
has  been  used  up,  the  blood  still  contains  sugar  which 
can  only  have  originated  from  the  proteids  of  the  body, 
fin- sugar  continues  to  be  used  by  the  tissues  and  yet 
does  not  disappear.  Glycogen  itself  may  be  formed  by 
the  liver  on  a  purely  proteid  diet,  and  this  is  not  sur- 
prising, for  proteids  appear  to  contain  a  carbohydrate 
radicle  in  their  constitution.  It  is  probable  that  the 
liver  having  stored  the  carbohydrate  excess  which  it  re- 
ceives during  absorption,  as  glycogen,  reconverts  this 
-tmv  into  sugar  as  it  is  needed  by  the  rest  of  the  body. 
That  the  liver  can  convert  glycogeu  into  sugar  is  cer- 
tain, for  it  may  be  caused  to  do  so  by  the  stimulation 
<•!'  afferent  nerves,  and  after  death  the  change  goes  on 
rapidly.  The  postmortem  change  may  be  prevented  by 
1>< »iling  the  liver  immediately  after  the  death  of  an  ani- 
mal, possibly  owing  to  the  destruction  of  a  ferment 
which  may  be  contained  within  the  cells  and  be  answer- 
aide  for  the  conversion.  Again,  by  injuring  the  floor 
<>t'  the.  fourth  ventricle,  the  liver  may  be  carfsed  to  dis- 
charge its  glycogen  as  sugar;  whether  the  result  is 
dm-  to  interference  with  the  circulation  of  blood  through 
the  liver,  or  whether  there  exists  in  the  bull)  a  definite 
center  which  regulates  the  metabolism  of  the  liver-cells, 
is  uncertain.  In  consequence  of  this  change  the  blood 
will,  for  the  time  being,  contain  an  excess  of  sugar,  which 
t  he  kidneys  at  once  begin  to  excrete,  giving  rise  to  Glyco- 
suria.  This  they  do  whenever  sugar  accumulates  in  the 
l)l«M>d  beyond  the  normal  amount — 0.1  to  0.2^.  The 
appearance  of  sugar  in  the  urine  does  not,  therefore,  indi- 
cate  an  abnormality  of  the  kidneys,  but  merely  that  they 


108  METABOLISM  AND  NUTRITION. 

are  discharging  their  normal  function  in  removing  from 
the  blood  an  excess  of  sugar,  for  the  occurrence  of  which 
they  are  not  answerable.  Sugar  may  accumulate  in  the 
blood  from  a  variety  of  causes ;  the  simplest  cause  is 
the  taking  of  abundant  carbohydrate  food,  but  it  is 
not  easy  in  this  way  to  produce  glycosuria  (sugar  in  the 
urine).  Disease  of  the  pancreas  often,  its  removal 
always,  causes  glycosuria,  but  this  has  nothing  to  do 
with  the  digestive  function  of  the  pancreatic  juice,  nor, 
apparently,  with  those  cells  of  the  pancreas  which  pro- 
duce this  secretion.  It  seems  probable  that  the  groups 
of  epithelioid  cells  which  are  known  as  Langerhans's 
bodies  play  an  important  part  in  regard  to  metabolism 
in  general.  Pancreatic  diabetes  continues  in  the  ab- 
sence of  carbohydrate  food,  and  even  during  starvation  ; 
the  sugar  in  this  latter  case  must  originate  from  the 
break-down  of  proteids.  Carbohydrate  food  increases 
pancreatic  glycosuria.  In  the  normal  condition  the 
pancreas  evidently  regulates  the  proteid  and  carbohy- 
drate metabolism  of  other  organs,  but  whether  through 
the  manufacture  of  some  substance  which  is  carried  to 
them  by  the  lymph  and  blood,  or  in  some  other  way,  is 
unknown.  In  the  absence  of  this  pancreatic  influence, 
either  more  proteid  than  usual  is  converted  into  sugar  or 
less  sugar  is  used  by  the  tissues ;  at  the  same  time  gly- 
cogen  disappears  from  the  liver.  The  liver  can,  how- 
ever, if  provided  with  levulose,  convert  this  form  of 
sugar  into  glycogen,  and  the  levulose  administered  does 
not  increase  the  glycosuria,  but  is  utilized  in  the  body. 
Fat,  after  absorption,  does  not  pass  through  the  liver 
before  entering  the  general  circulation.  There  is  no 
doubt  that  not  all  the  fat  of  the  food  can,  on  reaching 
the  cells  of  the  body,  be  simply  stored  in  the  form  in 
which  it  was  taken,  for  the  fat  of  different  animals 
varies  in  composition.  Human  fat  contains  a  larger 


PROTEID  METABOLISM.  109 

proportion  of  olein  than  does  mutton  or  beef  fat.  If 
mutton  or  beef  fat  is  to  be  stored,  the  excess  of,  for 
instance,  stearin  must  be  either  split  up  and  rearranged 
in  the  form  of  olein,  or  oxidized  and  excreted.  Under 
certain  conditions,  however,  some  foreign  fat  may  be 
stored  in  the  adipose  tissues  of  an  animal,  but  this  is 
unusual.  Not  all  the  fat  stored  in  the  body  is  derived 
from  the  fat  of  a  food;  a  small  proportion  may  be 
formed  from  sugar  or  glycogen,  and  probably  more  from 
proteid.  It  is  the  opinion  of  some  investigators  that 
;il  most  all  the  fat  of  the  food  is  oxidized  by  the  cells  as 
it  reaches  them,  and  that  very  little  is  stored  as  fat. 
Fat  affords  a  large  amount  of  energy  to  the  system, 
which  may  be  utilized  in  performing  mechanical  work, 
clu-inical  work  in  the  way  of  synthesis,  and  in  main- 
taining the  temperature  of  the  body.  The  final  prod- 
ucts  of  its  oxidation  are  carbon  dioxid  and  water. 

The  waste  products  of  proteid  metabolism  also  in- 
clude water  and  carbon  dioxid,  but  there  are  formed,  in 
addition,  nitrogenous  substances,  the  chief  of  which  is 
urea.  It  is  not  to  be  supposed  that  the  proteid  metab- 
olUm  which  goes  on  within  the  cells,  results  in  the  direct 
decomposition  of  proteid  into  urea,  carbon  djoxid,  and 
water,  for  in  the  muscles  which  contain  the  larger  pro- 
jx>rtion  of  body  proteids,  and  in  which  proteid  metab- 
oli>m  goes  on  continually,  little  or  no  urea  is  to  be 
found.  That  this  absence  of  urea  is  not  due  to  its 
rapid  removal  from  the  muscle  by  the  lymph  and  blood 
lias  been  proved  by  keeping  up  an  artificial  circulation 
through  the  vessels  of  a  dog's  hind  limbs,  the  bl<xxl 
being  oxygenated  and  passed  through  the  vessels  a  num- 
ber of  times.  Although  the  muscles  retained  their 
irritability,  showing  that  they  were  uninjured,  no  urea 
accumulated  either  in  the  muscle  or  blood.  Yet  since 
proteid  metabolism  undoubtedly  goes  on  in  the  muscles, 


110  METABOLISM  AND  NUTRITION. 

nitrogenous  waste  products  of  some  kind  must 
formed  there,  and  if  not  converted  into  urea  in  the 
muscles,  they  must  undergo  this  change  elsewhere  in 
the  body,  for  urea  is  the  main  nitrogenous  waste  product 
which  is  excreted.  Most  of  the  urea  appears  in  th 
urine,  but  that  it  is  not  formed  to  any  extent  by  th 
kidney  has  been  proved  by  circulating  oxygenated  bloo 
for  several  hours  through  the  vessels  of  an  extirpate 
kidney,  at  the  end  of  which  time  almost  no  urea  was 
found  in  the  blood.  Still  more  conclusive  evidence 
that  the  kidney  is  not  the  organ  chiefly  concerned  in 
the  production  of  urea  is  furnished  by  the  removal  of 
the  kidneys,  after  which  operation  urea  accumulates  in 
the  blood.  If  blood  be  circulated  through  the  limbs  of 
a  well-fed  dog,  and  then  through  the  liver  of  the  same 
animal,  these  organs  being  isolated  from  the  rest,  urea 
appears  in  the  blood.  On  its  passage  through  the  mus- 
cles of  the  limbs,  the  blood  takes  up  some  substance 
which,  on  subsequently  passing  through  the  liver,  is 
converted  into  urea.  That  the  liver  is  the  organ  in 
wrhich  most  of  the  urea  is  normally  produced  may  be 
shown  by  the  removal  of  the  liver,  or  by  excluding  it 
from  the  circulation.  The  urine  of  an  animal  whose 
blood  is  thus  prevented  from  passing  through  the  liver 
contains  very  little  urea,  showing  that  Avhile  urea  may 
be  formed  in  small  quantities  by  other  organs,  it  origi- 
nates for  the  most  part  in  the  liver.  In  the  absence  of 
the  liver,  urea  no  longer  forms  the  chief  nitrogenous 
waste  product ;  it  is  largely  replaced  by  ammonium 
salts.  This  indicates  that  the  liver  may  normally  con- 
vert these  ammonium  salts  into  urea,  and  that  it  pos 
sesses  this  power,  may  be  shown  by  circulating  through 
the  extirpated  liver  blood  to  which  has  been  added  the 
ammonium  salt  of  carbonic  acid,  carbamic  acid,  or  lac- 
tic acid ;  in  either  case  the  ammonium  salt  disappears 
and  its  place  is  taken  by  urea  ;  for  instance  : 


CREATIN.  Ill 

NH2.CO.ONH4  (NH2)2CO    -f    H,O. 

Alum,  Carbauiate  Urea 


Ammonium  carbamate  and  ammonium  lactatc  have 
been  found  in  blood  which  is  perfused  through  the  iso- 
lated hind  limbs  of  a  dog;  they  also  appear  in  the 
urine  of  an  animal  whose  blood  is  prevented  from  pass- 
ing througth  the  liver.  Glycocol,  the  second  of  the 
-cries  of  amido-fatty  acids  of  which  carbamic  or  amido- 
ti uiiiic  acid  is  the  first, 'may  also  be  converted  by  the 
liver  into  urea.  The  amido-acids,  such  as  leucin  and 
t\ rosin,  formed  in  the  intestinal  digestion  of  proteids 
an-  alter  absorption  carried  to  the  liver  and  probably 
changed  to  urea;  in  diseases  of  the  liver  leucin  and 
tyrnsin  may,  in  part,  take  the  place  of  urea  in  the  urine. 

Another  nitrogenous  waste  product  found  in  muscle 
i~  creatin  ;  this  is  probably  excreted  as  urea,  though  if 
carried  to  the  liver  as  creatin,  it  is  converted  into  and 
excreted  as  creatinin.  It  is  possible  that  creatin,  before 
leaving  the  muscle,  is  changed  to  ammonium  lactate, 
which  on  reaching  the  liver  is,  in  turn,  converted  into 
urea.  This  creatin  is  the  substance  which  gives  to  meat 
its  flavor;  it  may  be  extracted  by  boiling,  which,  if  pro- 
longed, leaves  the  meat  tasteless.  Creatin  isxrf  little  or 
no  value  as  food,  but  renders  the  meat  palatable  and 
may  act  as  a  stimulant. 

A  nitrogenous  waste  product  which  is  closely  related 
to  urea,  and  appeal's  in  the  urine  in  small  quantities,  is 
uric  acid.  On  examination  of  its  formula,  it  will  be 
>een  to  contain  two  urea  groups  united  with  a  central 
chain  of  C.C.CO: 

NH— C=O 
0=C        C— NIL 

I      II       >c=o 

NH— C-NHX 


112  METABOLISM  AND  NUTRITION. 

Through  oxidation  and  hydrolysis,  uric  acid  may  be 
decomposed,  with  the  formation  of  two  molecules  of  urea 
and  one  of  oxalic  acid.  If  urea  be  administered  to  a 
bird,  it  is  converted  by  the  liver  into  uric  acid ;  on  the 
other  hand,  uric  acid  administered  to  a  mammal  is  de- 
composed by  the  liver  with  the  formation  of  urea.  Th 
amount  of  uric  acid  found  in  human  urine  is  variable 
there  is  usually  one  part  of  uric  acid  to  about  thirty-iiv 
parts  of  urea,  but  the  ratio  varies  with  the  nature  of  the 
food.  The  amount  of  uric  acid  is  increased  by  nuclec 
proteid  food,  though  nuclein  does  not  seem  to  be  diges 
and  absorbed  to  more  than  a  small  extent.  It  has  bee 
stated  above  that  nuclein  may  be  split  up,  with  the  for 
mation  of  xanthin  bases,  which  are  closely  related  to 
uric  acid.  In  leukemia,  a  pathologic  condition  in  which 
the  number  of  leukocytes  in  the  blood  is  largely  in 
creased,  the  excretion  of  uric  acid  is  also  increased,  per 
haps  owing  to  the  break-down  of  leukocytes  in  unusu 
numbers,  and  the  liberation  of  their  nucleoproteid,  whic 
is  then  converted  into  uric  acid.  Not  all  the  uric  aci 
formed  in  the  body  may  be  expected  to  appear,  as  such, 
in  the  excretions,  for  much  of  it  is  probably  convertec 
into  urea ;  the  uric  acid  of  the  urine  has  perhaps  reachec 
the  kidneys  without  passing  through  the  liver. 

Hippuric  acid  is  a  nitrogenous  waste  product  whidj 
appears  in  human  urine  in  small  quantities  only ;  it 
more  abundant  in  the  urine  of  the  herbivora,  and,  in  th( 
case  of  man,  may  be  increased  by  eating  vegetables 
more  especially  fruits,  which  contain  aromatic  substances 
that  are  oxidized  in  the  body,  with  the  formation  of  ben 
zoic  acid.  Hippuric  acid  appears  in  the  urine,  to  a  cer 
tain  extent,  even  during  starvation,  and  cannot  therefore 
be  entirely  derived  from  food ;  aromatic  compounds 
must  originate  in  small  quantities  from  the  metabolism 
of  proteids,  and  be  converted  into  benzoic  acid.  The 


HIPPURIC  ACID.  113 

benzole  acid,  whether  it  be  formed  from  food  or  from 
body  proteids,  is  combined  by  the  kidney  with  glycocol 
to  form  hippuric  acid,  and  thus  excreted. 

It  appears,  then,  that  urea  is  not  an  immediate  prod- 
uct of  proteid  metabolism,  but  that  intermediate  sub- 
stances  are  formed,  such  as  creatin,  ammonium  salts, 
]><  tssibly  amido-acids,  etc.  It  is  certain  that  glycocol  may 
be  formed  in  the  body,  for  the  administration  of  ben- 
zole acid  results  in  the  appearance  of  hippuric  acid  in  the 
urine.  As  in  the  case  of  the  nitrogenous,  so  in  the  case 
of  the  carbonaceous  half  of  proteid,  decomposition  into 
the  final  waste  products,  carbon  dioxid  and  water,  is  not 
immediate.  Indeed,  after  a  meal  consisting  of  proteids, 
the  excretion  as  urea  of  an  amount  of  nitrogen  corre- 
sponding to  that  administered  is  accomplished  earlier 
than  the  excretion  of  the  amount  of  carbon  and  hydro- 
gen contained  in  the  proteid.  This  indicates  that  the 
proteid  is  split  into  a  nitrogenous  and  a  nonnitrogenous 
part,  the  latter  being  perhaps  transformed  into  glycogen, 
dextrose,  or  fat  before  it  is  utilized  by  the  cells.  It  is 
known  that  these  substances  may  be  formed  from  pro- 
teid food,  as  has  been  stated  above.  It  seems  probable 
that  fats  and  carbohydrates  never  form  part  of  the  bio- 
plasm, but  are  held  closely  in  contact  with  it  within  the 
cells,  and  utilized  by  it  as  a  source  of  energy.  Some  of 
the  proteid  food  is  undoubtedly  transformed  into  the 
living  proteid  of  bioplasm,  but  it  is  unlikely  that  it  all 
undergoes  this  process  before  being  oxidized.  In  all 
likelihood,  the  fats,  the  carbohydrates,  and  most  of  the 
proteid,  after  entering  the  cell,  suffer  decomposition 
without  ever  becoming  a  part  of  bioplasm.  Some  of 
their  decomposition  products  may  subsequently  undergo 
synthesis ;  for  example,  sugar  may  in  this  way  be  trans- 
formed into  fat.  The  proteid  of  bioplasm,  or,  as  it  is 
called,  tissue  proteid,  may  be  supposed  to  break  down 
8 


114  METABOLISM  AND  NUTRITION. 

but  slowly ;  at  the  rate,  it  has  been  estimated,  of  about 
1  <f0  per  diem. 

By  far  the  greater  part  of  the  proteid  metabolism 
occurs  in  the  muscles,  and  the  most  characteristic  fea- 
ture of  muscle  is  its  power  of  contraction,  yet  no  rela- 
tion exists  between  muscular  activity  and  proteid  metab- 
olism. Muscular  work  is  accomplished  at  the  expense 
of  the  nonnitrogenous  food-stuffs,  namely,  carbohy- 
drates and  fats ;  for  the  excretion  of  nitrogen  is  hardly 
affected  by  exercise,  unless  it  be  very  violent,  or  unless 
there  be  a  scarcity  of  fats  and  carbohydrates  in  the  diet. 
On  the  other  hand,  muscular  exercise  is  accompanied  by 
a  great  increase  in  the  excretion  of  carbon  dioxid.  Not 
all  the  energy  liberated  during  contraction  appears  in 
the  form  of  mechanical  work  ;  the  larger  portion  is  given 
off  as  heat.  In  the  absence  of  a  sufficient  supply  of 
nonproteid  material,  muscle  is  capable  of  utilizing  pro- 
teid as  a  source  of  mechanical  energy. 

Internal  Secretion. — Secretions  are  the  products  of 
glandular  activity  and  are  given  off  by  a  structure 
composed  of  one  or  more  gland  cells,  epithelial  in  char- 
acter, and  are  discharged  upon  a  free  epithelial  surface, 
such  as  the  skin  or  mucous  membrane,  or  upon  the 
closed  endothelial  surfaces  of  blood-  and  lymph-cavi- 
ties, in  the  first  instance  the  product  being  known  as 
an  external  secretion,  and  in  the  second  case  as  an  in- 
ternal secretion. 

The  internal  secretions  best  understood  are  the  secre- 
tions of  the  thyroid,  adrenal,  and  pituitary  glands,  a 
secretion  of  the  pancreas  other  than  the  pancreatic 
juice,  and  the  secretion  of  the  liver  which  modifies  gly- 
cogen  to  the  form  of  carbohydrate  circulating  in  the 
blood.  The  testes  and  the  ovaries  are-  also  supposed  to 
give  off  internal  secretions.  We  have  seen  that  the 
pancreas  exerts  an  important  influence  over  the  proteid 


INTERNAL  SECRETION.  115 

and  carbohydrate  metabolism  of  other  organs,  but  this  is 
not  the  only  instance  of  the  kind.  The  thyroid  body 
is  essential  to  the  normal  metabolism  of  the  nervous 
.-  v  - 1  cm.  If  the  thyroid  be  completely  removed  from  a  dog, 
the  animal  soon  dies ;  but  before  death  ensues  there  appear 
muscular  tremors,  spasms,  and  convulsions,  which  are  of 
cent  iid  origin,  depending  apparently  upon  abnormal  met- 
al x  >1  ism  in  the  cells  of  the  spinal  cord.  Monkeys  survive 
the  operation  longer;  they  also  show  muscular  tremors, 
and  myxedema  may  follow.  Myxedema  is  a  condition 
associated  in  man  with  atrophy  of  the  thyroid ;  the 
symptoms  are  an  overgrowth  of  the  subcutaneous  con- 
nective tissue,  muscular  weakness,  sometimes  spasms, 
and  mental  failure.  The  congenital  form  is  known  as 
cretinism,  the  child  being  idiotic  and  deformed.  In 
man  the  removal  of  the  thyroid  is  sometimes  followed 
by  myxedema,  this  variety  being  known  as  operative 
myxedema,  or  cachexia  strumipriva.  The  symptoms 
may  l>e  relieved  by  injecting  an  extract  made  from  the 
thyroid  of  some  other  animal  into  a  vein  or  under  the 
skin,  or  even  by  the  administration  of  raw  thyroid  with 
the  food.  The  normal  thyroid  evidently  produces  a 
snl  (stance,  or  substances,  which  enter  the  lymph  and 
blood,  are  carried  throughout  the  system,  and  take  effect 
more  especially  on  the  central  nervous  system.  In  the 
absence  of  these  substances,  the  metabolism  of  the  nerve- 
eel  Is  becomes  abnormal,  but  may  be  rectified  by  the 
administration  of  thyroid  extract.  The  overgrowth  of 
subcutaneous  connective  tissue  is  also  due  to  abnormal 
metabolism.  The  thyroid  produces  an  iodin  compound, 
known  as  iodothyrin,  or  thyroiodin,  which  appears  to  be 
one  of  the  substances  answerable  for  thyroid  influence, 
tor  this  product  is,  on  injection,  effective  in  relieving 
the  symptoms  of  myxedema.  It  is  possible  that  this 
irland  also  possesses  the  power  of  neutralizing  poisonous 


116  METABOLISM  AND  NUTEITION. 


products  of  normal  metabolism.  The  irritability  of  the 
cardie-inhibitory  and  depressor  nerves  is  reduced  by  the 
removal  of  the  thyroid,  and  increased  by  the  injection 
of  iodothyrin,  which  tends  also  to  lessen  the  irritability 
of  the  vasoconstrictors. 

The  removal  of  the  pituitary  body  is,  in  dogs,  fol- 
lowed by  symptoms  very  similar  to  those  seen  on 
removal  of  the  thyroid.  In  man,  however,  disease  of 
the  pituitary  body  is  not  accompanied  by  myxedema, 
but  by  an  overgrowth  of  the  bones  of  the  face  and 
limbs  ;  a  condition  named .  acromegaly.  Injection  of 
extracts  made  from  the  posterior  lobe  into  the  vessels 
causes  strengthening  of  the  heart-beat  and  constriction 
of  the  arteries,  apparently  influencing  directly  the  mus- 
cular coats  of  the  vessels. 

In  dogs  the  removal  of  both  adrenal  bodies,  or  supra- 
renal capsules,  is  more  quickly  fatal  than  is  the  removal 
of  either  the  thyroid  or  the  pituitary  body.  The  symp- 
toms which  precede  death  are  extreme  muscular  weak- 
ness, weak  heart-beat,  and  loss  of  vascular  tone.  In 
man  a  condition  known  as  Addison's  disease  is  asso- 
ciated with  abnormality  of  the  adrenals.  The  symp- 
toms are  similar  to,  but  less  acute  than,  those  following 
the  removal  of  the  bodies ;  in  addition,  there  occurs  a 
peculiar  bronzing  of  the  skin,  and  sometimes  of  the 
mucous  membranes.  Dogs  die  too  soon  for  this  symp- 
tom to  develop,  but  in  rabbits,  which  survive  the  oper- 
ation longer,  pigmentation  of  the  skin  has  occurred. 
Very  marked  eifects  are  produced  in  normal  animals  by 
the  intra vascular  injection  of  adrenal  extracts.  Mus- 
cular contraction  is  unusually  prolonged,  an  effect  resem- 
bling that  of  veratrin.  The  cardie-inhibitory  center  is 
strongly  stimulated,  the  auricle  ceases  to  contract,  and 
the  ventricle  beats  slowly ;  nevertheless  the  arterial 
blood  pressure  rises,  owing  to  a  direct  stimulation  of  the 


NUTRITION.  117 

art  orioles.  This  effect  is  transitory  but  energetic;  if 
the  vagi  have  been  previously  divided,  the  pressure  rises 
to  a  uTeat  height.  Extracts  made  from  the  cortical  por- 
tion of  the  gland  are  inert;  the  active  principle  is  to  be 
obtained  from  the  medullary  portion  only.  A  substance, 
epinephrin,  which  has  been  isolated  from  the  extract, 
produces,  on  injection,  the  characteristic  effects,  and  is 
evidently  one  of  the  active  principles  of  the  gland,  though 
perhaps  not  the  only  one.  We  may  conclude,  then,  that 
the  adrenal  body  elaborates  epinephrin,  and  perhaps 
other  substances,  which  pass  into  the  circulation  and 
art  on  muscular  tissue — skeletal,  cardiac,  and  vascular 
—in  such  a  manner  that  its  tone  is  increased  ;  in  other 
words,  they  hasten  muscular  metabolism,  perhaps  more 
especially  in  regard  to  the  oxidation  of  carbohydrates. 
In  the  absence  of  this  influence  the  muscles  lose  their 
tone. 

NUTRITION. 

The  body  is  constantly  liberating  energy  supplied  by 
the  food,  in  which  it  has  been  stored  by  the  plant ;  the 
ultimate  source  of  this  energy  being  the  light  and  heat 
of  the  sun.  The  question  to  be  discussecj,  is,  whether 
the  different  food-stuffs  are  of  equal  importance,  and 
whether  they  are  all  necessary  to  the  maintenance  of 
life.  It  may  be  mentioned,  in  the  first  place,  that  di- 
gestion goes  on  more  readily  on  a  mixed  diet.  In  all 
experiments  on  nutrition  it  is  necessary  to  keep  an  ex- 
aet  account  of  the  amount  and  quality  of  both  the  food 
and  the  excreta.  In  this  connection  it  is  usually  suffi- 
cient, as  far  as  the  proteids  are  concerned,  to  estimate 
the  amount  of  nitrogen  excreted  in  the  urine  and  feces. 
Proteids  contain,  by  weight,  from  15^  to  17  %  nitro- 
gen ;  consequently,  the  appearance  of  1  gram  of  nitro- 
gen in  the  excreta  indicates  the  decomposition  of  about 


118  METABOLISM  AND  NUTKITION. 

6.25  grams  of  proteid.  If  the  nitrogen  excreted 
exactly  equals  the  amount  taken  in  the  food,  the  animal 
is  said  to  be  in  a  condition  of  nitrogenous  equilibrium. 
If  the  excreta  contain  less  nitrogen  than  was  taken  in 
the  food,  nitrogen  has  been  stored  in  the  body ;  that  is, 
proteid  has  been  laid  up.  If  more  nitrogen  appears  in 
the  excreta  than  was  contained  in  the  food,  the  excess 
must  have  been  derived  from  the  break-down  of  an  un- 
usual amount  of  body  proteids.  Even  if  nitrogenous 
equilibrium  is  maintained,  the  weight  of  the  body  may 
not  remain  constant,  for  carbon  equilibrium  does  not 
always  accompany  an  equilibrium  in  nitrogen.  Carbon 
is  contained  in  all  classes  of  food-stuif,  and  while  a 
condition  of  nitrogenous  equilibrium  exists,  glycogen 
or  fat  may  be  stored  up  even  on  a  purely  proteid  diet, 
leading  to  a  deficit  in  the  carbon  excreted.  On  the 
other  hand,  fat  or  glycogen  may  be  used  up,  and  thus 
lead  to  the  excretion  of  an  excess  of  carbon,  without 
interfering  with  the  maintenance  of  nitrogenous  equilib- 
rium. It  is  therefore  necessary,  in  making  experiments 
on  the  relative  value  or  the  fate  of  the  food-stuffs,  to 
estimate  not  only  the  nitrogen,  but  also  the  carbon  of 
the  food  and  excreta. 

During  starvation  metabolism  does  not  cease,  but 
goes  on  entirely  at  the  expense  of  the  carbohydrates, 
fats,  and  proteids  of  the  body.  After  using  up  a  certain 
proportion  of  this  store,  the  animal  dies;  the  period 
which  lapses  before  death  depending  largely  on  the 
condition  of  the  animal  when  starvation  began.  A 
lean  animal  will  usually  withstand  the  loss  of  about 
0.4  of  its  body-weight ;  one  that  is  fat  may  live  until 
its  weight  has  been  reduced  by  0.5  ;  an  adult  human 
being  may  live  for  three  weeks  without  food  if  supplied 
with  water  ;  children  die  in  a  few  days,  after  losing  about 
0.25  of  their  weight,  Fat  disappears  rapidly  during 


NUTRITION.  119 

starvation  ;  the  proteids,  as  long  as  fat  is  being  utilized, 
diminish  very  slowly.  When  most  of  the  fat  has  been 
cni i snmed  the  body  falls  back  upon  its  store  of  pro- 
teids, and  the  excretion  of  urea  is  suddenly  increased 
beyond  that  of  the  preceding  period.  While  the  fat 
la-ts,  the  proteids  are  not  used  to  any  extent  as  a 
source  of  energy  for  the  maintenance  of  temperature  or 
i'or  muscular  work ;  but  when  the  supply  of  fat  has  been 
exhausted,  they  must  be  so  used;  and  even  before  this 
Man-e  is  reached,  proteid  must  be  decomposed  in  the  for- 
mation of  sugar,  which  never  disappears  from  the  blood. 
A-  starvation  progresses  metabolism  diminishes,  and 
tin-  loss  of  weight  grows  less  from  day  to  day.  The 
greatest  loss  in  weight  is  sustained  by  the  adipose  tissue ; 
then  come  the  muscles  ;  next  the  liver,  spleen,  etc.,  and, 
lastly,  the  heart  and  central  nervous  system,  which 
suffer  almost  no  loss,  for  they  live  at  the  expense 
»»f  the  other  tissues.  It  might  be  supposed  that  a 
daily  supply  of  proteid  food,  equal  in  quantity  to  the 
amount  of  tissue  proteid  which  is  broken  down  per 
diem  during  starvation,  would  suffice  to  keep  an  animal 
in  a  condition  of  nitrogenous  equilibrium,  but  this  is  far 
from  being  the  case.  This  depends  uptpi  the  fact 
that  proteid  metabolism  within  the  cells  is  stimulated 
by  the  reception  of  proteid  food ;  the  larger  the  quantity 
of  proteid  food  which  reaches  the  tissues,  the  more 
rapidly  does  proteid  metabolism  go  on,  and,  as  a  result 
of  this,  the  cells  are  capable  of  using  practically  all  the 
proteid  which  is  supplied  to  them.  In  one  classic  ex- 
periment a  dog,  during  starvation,  was  found  to  con- 
sume his  store  of  muscle  at  the  rate  of  165  grams  per 
diem;  at  the  same  time  he  was  burning  up  95  grams 
of  fat.  When  given  500  grams  of  lean  meat,  the 
nitrogen  in  his  urine  showed  that  599  grams  were  de- 
composed ;  that  is,  that  he  had  used  lip  99  grams  of 


120  METABOLISM  AND  NUTRITION. 


muscle  in  addition  to  what  he  had  received.  At  the 
same  time  47  grams  of  fat  were  oxidized.  In  one  day  of 
starvation  the  animal  had  lost  in  weight  260  grams  ;  the 
administration  of  500  grams  of  meat  only  reduced  this 
loss  to  146  grams.  On  gradually  increasing  the  amount 
of  proteid  food,  from  day  to  day,  it  was  not  until  1500 
grams  of  meat  were  given  that  loss  of  weight  was  pre- 
vented ;  at  this  point  nitrogenous  equilibrium  was  es- 
tablished, and  4  grams  of  fat  were  stored  up.  In- 
creasing the  amount  of  proteid  food  still  further  did  not 
lead  to  an  appreciable  storing  up  of  proteid  tissue ;  in 
fact,  when  2500  grams  were  given,  2512  grams  were 
decomposed,  a  loss  of  muscle  to  the  extent  of  1 2  grams. 
Fat  was,  however,  stored  up  to  the  extent  of  57  grams. 
Thus,  if  kept  on  a  purely  proteid  diet  an  animal  must, 
in  order  to  maintain  nitrogenous  equilibrium,  receive  a 
certain  amount  of  food ;  if  more  than  this  be  given,  it 
does  not  lead  to  the  storing-up  of  the  excess,  for  the 
cells  become  spendthrift  and  burn  up  all  the  proteid 
that  they  receive,  in  this  way  maintaining  nitrogenous 
equilibrium  at  a  higher  level. 

Proteid  metabolism  may,  however,  be  reduced  by  a 
mixed  diet.  In  the  case  of  the  animal  which  required 
1 500  grams  of  meat  for  the  maintenance  of  nitrogenous 
equilibrium,  an  addition  of  150  grams  of  fat  to  this 
amount  of  meat  resulted  in  the  building-up  of  tissue  to 
the  extent  of  26  grams.  Further  than  this,  if  150 
grams  of  the  fat  was  given,  the  amount  of  proteid  neces- 
sary was  much  less  ;  under  these  circumstances  the  allow- 
ance of  meat  was  reduced  to  800  grams  without  the  ap- 
pearance of  an  excess  of  nitrogen  in  the  urine.  There- 
fore, a  mixed  diet  is  the  more  economic,  for  proteid 
is  the  most  expensive  of  foods ;  it  is  better  physiologi- 
cally, for  digestion  is  much  less  likely  to  become  dis- 
ordered. Carbohydrates  are  even  more  effective  than 


NUTRITION.  121 

fats  in  the  reduction  of  proteid  metabolism  ;  gelatin 
serves  this  purpose  better  than  either.  If,  then,  it  is 
desired  to  reduce  proteid  metabolism  as  far  as  possible, 
in  order  that  there  may  be  a  building-up  of  tissue  pro- 
teid,— of  muscle,  for  example, — it  is  best  to  give  but  a 
moderate  amount  of  proteid,  with  a  good  proportion  of 
one  of  the  other  foods,  or,  better  still,  a  mixture  of  all 
the  others.  A  mixture  of  the  other  foods,  no  matter 
hu\\  abundant  the  diet,  will  not,  in  the  absence  of  pro- 
lei*  1  food,  serve  to  maintain  nitrogenous  equilibrium; 
life  will  be  prolonged,  but  death  from  proteid  starvation 
is  inevitable. 

There  is  a  difference  of  opinion  as  to  the  relative  pro- 
portions in  which  the  food-stuffs  should  be  combined  to 
form  an  ideal  diet.  The  following  is  the  diet  recom- 
mended by  Voit,  and  is  intended  for  a  man  of  70  kilo- 
grams : 

Proteid,  118  grams.       Fat,  56  grams.      Carbohydrates,  500  grams. 

This  diet  is  supposed  to  consist  of  both  animal  and 
vegetable  food,  and,  consequently,  cannot  be  expected 
to  be  absorbed  in  toto,  for  vegetable  food  is /I ess  readily 
digested  than  meat,  owing  chiefly  to  the  cellulose  cover- 
ing. 

In  order  to  calculate  the  amount  of  energy  supplied  to 
the  body  by  a  given  diet,  we  must  know  the  combustion 
equivalent  of  each  food-stuff;  this  is  determined  by 
burning  the  substance  in  question,  and  measuring  the 
ln-at  given  off.  In  the  case  of  fats  and  carbohyd rates, 
the  same  amount  of  energy  is  liberated  within  the  body 
as  when  the  substance  is  burned  outside  the  Inxly,  for 
the  oxidation  is  in  each  case  complete,  the  final  products 
of  combustion  being  carbon  dioxid  and  water.  Not  all 
the  energy  contained  in  proteids  is  set  free  within  the 


122  METABOLISM  AND  NUTRITION. 

body,  for  the  end-products  of  proteid  metabolism  are,  in 
the  main,  carbon  dioxid,  water,  and,  instead  of  nitrogen, 
urea,  which  is  capable  of  undergoing  oxidation  and 
liberating  energy.  Besides  urea,  other  oxidizable  sub- 
stances are  formed  in  small  quantities,  and  we  must  de- 
duct the  energy  thus  lost  to  the  body  from  that  intro- 
duced in  proteid.  The  potential  energy  of  a  substance 
is  expressed  in  calories.  A  calorie  is  the  amount  of 
heat  required  to  raise  the  temperature  of  1  gram  of  water 
by  1°  C.  The  potential  energy  available  to  the  body 
from  1  gram  of  proteid  is  4100  calories  ;  from  1  gram 
of  fat  9300  calories  ;  and  from  1  gram  of  carbohydrate, 
4100  calories.  Adopting  Voit's  diet,  as  given  above, 
the  available  energy  will  be  : 

Proteid,  118  grams  X  4100         .    .     483,800 

Fat,  56  grams  X  9300 520,800 

Carbohydrate,  500  grams  X  4100  .  2,050,000 

3,054,600  calories. 

This  represents  a  diet  suitable  for  a  man  doing  ordinary 
work ;  increased  labor  entails  the  necessity  of  a  larger 
food  supply.  As  muscular  work  is  performed  almost 
entirely  at  the  expense  of  the  nonnitrogenous  foods,  it 
would  seem  rational  to  vary  the  diet  by  increasing  the 
proportion  of  these  when  more  work  is  to  be  done ;  ex- 
perience has  shown,  however,  that  it  is  better  to  give 
more  proteid  also.  The  metabolism  of  the  nonnitrog- 
enous foods  is  also  increased  by  exposure  of  the  body  to 
cold  ;  that  of  proteids  is  not  affected  to  an  appreciable 
extent.  The  combustion  equivalent  of  fat  is  higher 
than  that  of  the  other  foods,  and  dwellers  in  cold  cli- 
mates are  said  to  have  a  craving  for  fatty  food,  but  there 
is  no  proof  that  fat  is  more  readily  used  by  the  muscles 
in  keeping  up  the  temperature  of  the  body. 

Inorganic  salts  form  as  essential  a  part  of  the  diet  as 


NUTRITION.  123 

the  foods  which  supply  energy  to  the  body.  It  has  been 
shown  that  an  animal  fed  on  food  from  which  the  inor- 
ganic salts  have  been,  as  far  as  possible,  removed  dies 
Sooner  than  similar  animals  which  are  starved.  Inor- 
ganic salts  are  necessary  for  the  neutralization  of  acids 
funned  during  metabolism  ;  for  instance,  sulphuric  acid, 
which  originates  from  the  oxidation  of  the  sulphur  con- 
tained in  the  proteid  molecule.  It  is  true  that  this  may, 
to  a  certain  extent,  be  neutralized  by  ammonia,  also 
split  off  from  proteid.  This  is  by  no  means  the  only 
use  of  the  inorganic  salts,  and,  of  course,  neutral  salts, 
such  as  sodium  chlorid,  are  not  used  in  this  way. 
Amongst  the  uses  of  the  inorganic  salts  in  the  body 
may  be  mentioned  the  following :  they  maintain  the 
alkalinity  of  the  blood  and  lymph,  which  is  of  the 
utmost  importance,  for  an  acid  reaction  rapidly  destroys 
the  irritability  of  bioplasm;  they  are  of  importance  in 
regard  to  the  osmotic  pressure  of  the  liquids  and  cells 
<>f  the  body  ;  their  presence  is  necessary  to  the  solution 
of  the  globulins;  from  sodium  chlorid  is  derived  the 
clilorin  for  the  formation  of  hydrochloric  acid  in  the 
gastric  glands;  sodium  chlorid,  potassium  salts,  and 
soluble  calcium  salts  are  necessary  to  the  activity  of  the 
heart ;  calcium  salts  are  concerned  in  the  clotting  of 
blood,  and  so  on.  It  would  appear  that  the  inorganic 
salts  of  the  food  must,  to  a  certain  extent,  be  in  combi- 
nation with  organic  substances,  such  as  proteid;  other- 
wise, they  do  not  fulfill  all  that  is  required  of  them.  A 
vegetable  diet  contains  an  excess  of  potassium  salts,  and 
seems  to  necessitate  a  supply  of  sodium  chlorid,  for  the 
potassium  salts  react  to  some  extent  with  the  sodium 
chlorid  of  the  blood,  forming  potassium  chlorid  and,  for 
instance,  sodium  phosphate;  this  loss  of  sodium  chlorid 
to  the  blood  must  be  made  good  by  its  addition  to  the 
food.  A  supply  of  calcium  for  the  building-up  of 


124  METABOLISM  AND  NUTRITION. 

bone  is  needed  especially  by  growing  children,  and  this 
want  is  particularly  well  supplied  by  milk,  which  con- 
tains an  abundance  of  calcium.  Iron  is  another  sub- 
stance which  is  needed,  chiefly  in  relation  to  the  forma- 
tion of  hemoglobin ;  this  is  supplied  in  combination  with 
nucleo-albumins  in  the  food,  but  inorganic  salts  of  iron 
may  be  absorbed.  A  diet  consisting  entirely  of  milk  is 
unsuitable  for  any  but  infants,  for  it  contains  an  insuffi- 
cient quantity  of  iron.  The  infant  contains  within  its 
tissues  a  store  of  iron  which  is  slowly  used  up  during 
the  period  of  suckling ;  if  confined  to  a  milk  diet  beyond 
the  usual  time,  it  becomes  anemic. 

Water  supplies  no  energy  to  the  body,  but  is  indis- 
pensable, for  in  its  absence  metabolism  is  impossible.  It 
serves  as  a  solvent  for  both  food  and  excreta ;  in  the  re- 
moval of  the  latter,  large  quantities  of  water  are  elimi- 
nated, and  must  be  replaced.  The  evaporation  of  sweat 
is  a  most  important  means  of  resisting  the  effect  of  a 
high  temperature. 


QUESTIONS  FOR  CHAPTER  V. 

During  the  absorption  of  carbohydrates,  in  which  set  of  blood- 
vessels is  the  percentage  of  sugar  the  highest? 

How  may  glycogen  be  most  readily  caused  to  disappear  from  the 
muscles  ? 

Would  you  expect  to  cause  glycosuria  by  puncturing  the  med 
ulla  of  an  animal  which  had  for  some  time  been  fed  on  fat  ? 

Is  the  appearance  of  sugar  in  the  urine  a  necessarily  serious 
symptom  ? 

May  it  occur  in  health  ? 

How  is  the  percentage  of  sugar  in  the  body  increased  after  death  ? 

How  may  we  determine  whether  a  certain  substance  is  formed 
by  a  particular  organ  ? 

Compare  the  work  done  by  the  liver  on  a  proteid  diet  witli  thai 
done  on  a  carbohydrate  diet. 


QUESTIONS.  125 

1'nder  \\liat  circumstances  would  you  expect  an  accumulation 
of  urea  in  the  blood  ? 

1'nder  what  circumstances  would  you  expect  the  urea  of  the 
urine  to  be  replaced  by  ammonium  salts? 

Does  sleep  cause  a  variation  in  the  rate  of  nitrogenous  or  non- 
11  it  r<  t»t'iious  metabolism  ? 

Does  all  the  urea  which  appears  in  the  urine  originate  from  the 
break-down  of  tissue  proteids? 

From  what  nitrogenous  substances  may  urea  be  formed  by  the 
liver? 

Can  a  molecule  of  urea  be  formed  from  one  molecule  of  glycocol  ? 

"What  are  the  waste  products  of  muscular  metabolism? 

Which  is  the  more  nutritious,  soup  made  by  boiling  meat  or  the 
insoluble  residue? 

"Which  is  the  more  palatable?     Why? 

What  changes  occur  in  the  composition  of  a  calf's  urine  when  it 
is  weaned? 

Is  the  formation  of  fat  from  sugar  a  synthetic  or  an  analytic 
process? 

Mention  instances  of  synthesis  and  analysis  which  occur  during 
metabolism. 

Wliat  different  factors  prevent  an  accumulation  of  sugar  in  the 
blood? 

What  is  meant  by  internal  secretion  ? 

Distinguish  between  internal  and  external  secretion. 

What  is  the  physiologic  treatment  of  myxedema?x 

Compare  the  effect  of  injecting  epinephrin  into  the  vessels  of  two 
animals,  one  of  which  is  normal,  the  spinal  cord  of  the  other  having 
In  eu  previously  divided  at  the  level  of  the  seventh  cervical  nerves. 

By  what  operative  procedure  may  we  insure  the  highest  blood 
pressure  on  the  injection  of  epinephrin? 

Is  the  percentage  of  ammonia  in  the  urine  increased  by  the 
administration  of  ammonium  carbonate? 

How  may  it  be  increased  ? 

How  may  muscular  exercise  be  caused  to  increase  the  excretion 
of  urea? 

If  an  animal  receives  no  nitrogenous  food,  does  nitrogen  dis- 
appear from  the  urine? 


126  METABOLISM  AND  NUTRITION. 

What  organ  receives,  in  proportion  to  its  size,  the  smallest  arte- 
rial blood  supply? 

Do  all  the  end-products  of  hepatic  metabolism  enter  the  bile- 
ducts  ? 

Do  the  amounts  of  urea  and  uric  acid  in  the  urine  always  vary 
together  ? 

What  is  the  surest  means  of  increasing  proteid  metabolism? 

If  an  animal  be  kept  in  a  condition  of  nitrogenous  equilibrium, 
does  its  weight  necessarily  remain  constant  ? 

Can  an  animal  gain  in  weight  when  in  a  condition  of  carbon 
equilibrium  ? 

Is  it  possible,  by  giving  a  large  quantity  of  proteid  food,  to 
cause  the  appearance  of  proteid  in  the  urine? 

What  is  the  final  effect  of  an  abundant  diet  containing  an  in- 
sufficient amount  of  proteid? 

Supposing  that  an  animal  is  receiving  a  daily  allowance  of  200 
grams  of  proteid  food,  and  that  it  excretes  30  grams  of  nitrogen, 
and  60  grams  of  carbon,  what  are  we  to  conclude? 

If  an  animal,  on  a  diet  of  200  grams  of  proteid,  excretes  40 
grams  of  nitrogen,  and  120  grams  of  carbon,  what  are  we  to  con- 
clude? 

Under  what  circumstances  will  moderate  muscular  exercise 
cause  a  deficit  of  nitrogen  in  the  urine? 

Why  does  the  administration  of  a  mineral  acid  reduce  the  pro- 
portion of  nitrogen  which  is  excreted  in  the  form  of  urea? 

Under  these  circumstances,  how  is  this  nitrogen  excreted  ? 

To  what  kind  of  diet  is  the  addition  of  sodium  chlorid  of  most 
importance  ? 

During  starvation  the  heart  loses  but  little  weight.  Is  the  rate  of 
cardiac  metabolism  slow  as  compared  with  that  of  skeletal  muscle  ? 

In  choosing  a  diet  for  a  child  which  is  deprived  of  milk,  to  what 
inorganic  constituent  should  special  attention  be  paid  ? 

What  are  the  limitations  to  the  use  of  milk  as  the  sole  article  of 
diet? 


CHAPTER  VI. 

EXCRETION. 

THE  waste  products  of  metabolism, — carbon  clioxid, 
water,  urea,  and  other  substances  in  smaller  quantities, 
— the  water  and  inorganic  salts  that  are  absorbed  from 
the  alimentary  canal,  and  other  material  which,  though 
al>H>rbed,  undergoes  no  chemical  change  in  the  body,  are 
all  excreted  through  various  channels.  Carbon  dioxid 
is,  in  the  main,  excreted  by  the  lungs,  but  is  also  elim- 
inated, to  a  much  less  extent,  in  various  secretions, 
such  as  the  sweat,  saliva,  etc.  Only  a  small  proportion 
of  the  water  which  is  excreted  has  originated  in  the 
eniirsc  of  metabolism  ;  most  of  it  represents  that  which 
was  taken  through  the  mouth.  It  is  excreted  by  the 
glands  of  the  alimentary  canal ;  most  of  this,  however, 
is  reabsorbed.  It  is  also  excreted  by  the  lacrimal 
•  ••lauds,  and,  in  much  larger  quantities,  by  thfc  respira- 
tory mucous  membranes,  sweat  glands,  and  kidneys. 
Urea  is  found  in  traces  in  the  saliva,  bile,  intestinal 
juice,  and  milk,  but  by  far  the  majority  is  excreted  in 
the  urine. 

The  Urine. — The  chief  constituents  of  the  urine  are 
water,  urea,  uric  acid,  hippuric  acid,  xanthin  bases,  creat- 
i u iu,  conjugated  sulphates,  and  inorganic  salts.  The 
origin  of  these  substances  has  been  already  discussed. 
A 1  ><  >ut  30  grams  of  urea  is  excreted  per  diem,  the  amount 
varying  with  proteid  metabolism.  The  amount  of  uric 
aeid  is  also  variable,  the  average  being  about  0.8  gram ; 

127 


128  EXCRETION. 

it  depends  more  upon  the  quality  than  the  quantity  of  the 
food,  and  probably  upon  the  extent  of  cell  destruction ; 
it  is  increased  by  exercise,  and  diminished  by  rest. 
Free  uric  acid  is  not  found  in  fresh  urine ;  it  is  excreted 
in  the  form  of  the  more  soluble  urates ;  on  standing, 
these  may  be  converted  into  free  acid,  which  is  precipi- 
tated ;  this  occurs  most  readily  in  acid  urine,  and  is  due 
to  the  reaction  of  the  urates  with  the  acid  phosphates. 
The  xanthin  bases  include  xanthin,  hypoxanthin,  guanin, 
adenin,  etc.;  they  are  closely  related  to  uric  acid,  which 
may  be  formed  from  them  in  the  body.  About  0.1 
gram  xanthin  bases  is  excreted  per  diem.  The  crea- 
tinin  of  the  urine  is  derived  chiefly  from  the  creatin  of 
the  food,  and  varies  with  the  amount  so  taken,  the  aver- 
age excretion  being  about  1  gram  per  diem.  Hippuric 
acid  occurs  in  the  urine  to  the  extent  of  about  0.7  gram 
per  diem,  and  varies  with  the  amount  of  vegetable  food 
eaten.  The  conjugated  sulphates  have  been  mentioned 
in  speaking  of  proteid  putrefaction  in  the  large  intes- 
tine ;  conditions  which  favor  the  growth  and  activity  of 
bacteria  in  the  intestines  increase  the  amount  of  these 
substances  in  the  urine,  while  rendering  the  contents  of 
the  intestines  antiseptic  prevents  their  appearance.  The 
urinary  pigments  are  derived  directly  or  indirectly  from 
hemoglobin.  Not  the  whole  of  the  inorganic  constit- 
uents of  the  urine  are  derived  directly  from  the  food ; 
for  instance,  sulphuric  acid  and  phosphoric  acid  are 
formed  in  the  metabolism  of  proteids,  the  sulphates  of 
the  urine  originating,  for  the  most  part,  in  this  way,  the 
phosphates  to  a  less  extent.  Besides  sulphates  and 
phosphates,  there  are  present  carbonates  and,  in  larger 
quantity,  chlorids.  Sodium,  potassium,  magnesium,  and 
calcium  are  present ;  the  relative  quantity  of  each  is 
indicated  by  the  order  in  which  they  are  mentioned ; 
they  are,  of  course,  combined  as  salts. 


THE  SECRETION  OF  URINE.  129 

The  acidity  of  the  urine  is  not  due  to  the  presence  of 
five  acid,  but  to  the  acid  phosphates.  Both  acid  and 
alkaline  phosphates  are  present  in  the  urine,  the  former 
predominating.  The  degree  of  acidity  depends  upon 
several  factors ;  in  the  main,  it  represents  the  balance 
l)ct  \\een  the  available  bases  taken  in  the  food,  and  the 
acids  produced  in  metabolism.  The  secretion  of  the 
acid  gastric  juice  usually  decreases  the  acidity  of  the 
urine  secreted  during  gastric  digestion,  but  this  effect 
may  be  neutralized  by  the  secretion  of  the  alkaline  saliva, 
bile  and  pancreatic  juice.  Vegetable  food  contains,  in 
addition  to  alkalies,  salts  of  organic  acids,  which,  on 
oxidation,  are  converted  into  carbonates,  and  may  be 
used  in  neutralizing  the  acids  formed  during  metabolism  ; 
vegetable  food,  therefore,  reduces  the  acidity  of  the 
urine  ;  from  animal  food,  on  the  other  hand,  the  amount 
of  acid  formed  exceeds  the  available  bases,  and  the 
excess  is  neutralized  by  the  conversion  of  alkaline  into 
acid  phosphates.  The  specific  gravity  varies  from  1015 
to  1025,  and  depends  chiefly  upon  the  amount  of  liquid 
absorbed  by  the  alimentary  canal,  and  the  amount 
excreted  through  other  channels.  The  amount  of  food 
consumed  will,  of  course,  influence  the  quantity  of  solids 
excreted.  In  making  observations  on  the  specific  grav- 
ity of  the  urine,  it  is  best  to  collect  and  mix  the  whole 
amount  passed  in  twenty-four  hours,  beginning  with  an 
empty  bladder.  The  amount  varies  from  1200  to 
1700  c.c. 

The  secretion  of  urine  depends  chiefly  upon  the  blood 
supply  of  the  kidney.  The  kidney  receives  this  supply, 
through  the  short  renal  artery,  from  the  aorta ;  the  pres- 
sure in  the  first  set  of  capillaries — those  forming  the 
irlomerulus — being,  in  consequence  of  this  arrangement, 
high.  The  pressure  in  the  capillaries  of  the  kidney 
varies,  of  course,  with  the  strength  and  rate  of  the  heart- 
9 


130 


EXCRETION. 


beat;  it  also  varies  with  the  condition  of  the  arterioles 
in  other  parts  of  the  body,  and,  in  addition,  with  the 
state  of  its  own  arterioles.  The  kidney  will  receive  the 
most  abundant  supply  of  blood  when  the  heart-beat  is 
strong,  the  vessels  of  other  parts  constricted,  and  the 
local  arterioles  dilated.  Under  these  circumstances  the 
amount  of  urine  secreted  will  be  abundant.  In  cold 
weather  the  cutaneous  vessels  are  constricted  and  more 
blood  flows  through  the  abdominal  organs,  including  the 
kidney ;  in  cold  weather,  therefore,  more  urine  will  be 
secreted  than  when  it  is  warm,  for  in  the  latter  condi- 
tion the  kidney  receives  less  blood,  the  skin  more,  and 
the  blood  is  concentrated  by  the  free  secretion  of  sweat. 
The  kidney  vessels  are  controlled  by  the  central  ner- 
vous system,  through  both  vasoconstrictor  and  vaso= 
dilator  nerves  which  leave  the  spinal  cord  in  the  lower 
thoracic  nerves,  enter  the  sympathetic,  and  pass  through 
the  splanchnic  to  the  solar  ganglia,  where  they  probably 
.end  in  contact  with  cells  whose  nonmedullated  axons 
(post-ganglionic  fibers)  pass  along  the  renal  artery  to 
the  kidney.  A  division  of  these  nerves  results  in  a 
dilatation  of  the  renal  arterioles  and  an  increased  flow 
of  urine ;  their  stimulation  ordinarily  causes  vasocon- 
striction  and  lessened  secretion,  but  if  stimulated  with 
slowly  repeated  induction  shocks,  the  action  of  the  vaso- 
dilators is  called  into  play.  A  division  of  the  spinal 
cord  in  the  upper  thoracic  region  or  division  of  both 
splanchnics  leads  to  the  dilatation  of  so  many  vessels 
that  the  general  blood  pressure  is  reduced  to  a  point  at 
which  the  dilatation  of  the  kidney  arterioles  cannot 
result  in  an  increased  flow  of  blood  through  the  kidney. 
The  existence  of  a  double  set  of  capillaries  in  the  kid- 
ney offers  an  unusually  high  resistance,  and,  to  over- 
come this,  a  comparatively  high  blood  pressure  is 
necessary. 


THE  SECRETION  OF  URINE.  131 

We  <lo  not  know  precisely  how  the  urine  is  secreted, 
hut  the  water  and  inorganic  salts  are  probably  filtered 
through  the  walls  of  the  glomerular  capillaries  and 
cpit helium  of  the  capsule.  The  conditions  are  very 
favorable  to  filtration,  for  the  blood  pressure  in  the 
capillaries  is  high  and  that  in  the  capsule  must  be  low, 
a-  there  is  a  free  exit  for  the  urine  through  the  tubules. 
The  filtration  hypothesis  has  been  disputed  on  the 
ground  that  ligation  of  the  renal  vein,  while  it  must 
raise  the  intracapillary  pressure  and  thus  favor  filtration, 
nevertheless  puts  a  stop  to  the  secretion  of  urine.  This, 
however,  may  not  be  a  valid  objection,  for  the  distention 
of  the  veins  which  results  probably  compresses  the 
renal  tubules,  and,  by  preventing  the  exit  of  the  urine, 
raises  the  pressure  in  the  capsule  toward  that  in  the 
capillaries.  The  capsular  epithelium  may  be  supposed 
to  act  like  a  gelatin  membrane,  through  which  the  water 
and  salts  of  blood-serum  may  be  filtered,  leaving  behind 
tin  proteids.  In  such  a  case  the  resistance  to  filtration 
«!"!•>  not  consist  only  in  that  offered  by  the  membrane 
to  the  passage  of  water  and  salts,  for  the  proteids,  owing 
to  the  osmotic  pressure  which  they  exert,  tend  to  retain 
water  and  to  prevent  its  escape  from  the  serum.  The 
proteids  of  plasma  exert  an  osmotic  pressure  of  from  25 
to  ;}()  mm.  of  mercury  ;  this,  then,  must  be  added  to  the 
r< >i  stance  which  is  offered  by  the  membrane  to  filtration 
of  water  and  salts.  Thus,  to  cause  filtration  a  some- 
what greater  force  is  needed,  and  it  has  been  found  that 
the  secretion  of  urine  ceases  when  the  blood  pressure 
falls  below  40  mm.  of  mercury  ;  it  also  ceases  when  the 
pressure  in  the  capsule  has  been  raised  to  within  40  or 
50  mm.  Hg  of  that  in  the  capillaries. 

The  urine  as  it  leaves  the  kidney  is  a  very  different 
liquid  from  any  that  could  result  from  the  mere  filtra- 
tion of  blood  plasma ;  if,  then,  filtration  goes  on  into 


132  EXCRETION 

the  capsule,  this  filtrate  must  be  greatly  modified  as  it 
passes  through  the  tubule  toward  the  pelvis  of  the  kid- 
ney. This  undoubtedly  takes  place,  for  the  more  rap- 
idly the  urine  passes  through  the  tubules,  the  less  it  is 
modified,  and  the  more  it  resembles  the  plasma  in  com- 
position and  reaction.  When  it  traverses  the  tubules 
more  slowly,  time  is  given  for  its  concentration,  appar- 
ently by  the  absorption  of  water.  If  water  is  absorbed 
from  the  glomerular  filtrate  by  the  cells  which  line  the 
tubule,  they  perform  an  immense  quantity  of  work,  for 
the  osmotic  pressure  of  the  urine  is  much  greater  than 
that  of  the  blood  plasma.  In  one  case  the  osmotic 
pressure  of  the  urine  of  a  cat  which  had  been  deprived 
of  water  was  greater  than  that  of  its  blood  plasma  by 
498  meters  of  water ;  and  the  tubule  cells,  in  transfer- 
ring water  from  urine  of  this  density  to  the  blood 
plasma,  must  have  exerted  a  tremendous  force.  The 
cells  of  which  the  convoluted  tubules  are  formed  are 
much  more  highly  developed  than  those  which  line  the 
capsule,  and  we  may  expect  them  to  be  more  specialized 
in  function.  It  seems  probable  that  uric  acid  is  excreted 
in  this  portion  of  the  tubule ;  experiment  has  proved 
that  such  is  the  case  in  birds.  With  regard  to  the  ex- 
cretion of  the  more  soluble  urea,  we  have  no  knowledge 
as  to  whether  it  occurs  in  the  capsule  or  tubules ;  we 
might  expect  that  it  would  accompany  the  inorganic 
salts  and  water  through  the  wall  of  the  capsule.  The 
urine  as  it  leaves  the  capsule  is  alkaline  in  reaction,  re- 
sembling the  plasma  in  this  respect ;  on  its  passage 
through  the  tubules  it  becomes  acid,  either  through  the 
addition  of  acid  phosphates  or  the  removal  of  alkalies. 
Temporary  ligation  of  the  renal  artery  prevents  the 
secretion  of  urine  not  only  during  the  period  of  occlu- 
sion, but  for  some  little  time  after  the  circulation  is  re- 
established. Some  take  this  as  proof  that  filtration  is 


THE  SECRETION  OF  URINE.  133 

not  answerable  for  the  glomerular  secretion.  It  is  easy 
to  see  how  this  might  incapacitate  the  tubule  cells  for 
the  performance  of  work,  but  why  it  should  put  a  stop 
to  filtration  is  obscure;  the  glomerular  epithelium  is  in 
some  way  rendered  less  permeable.  That  the  epithelium 
of  some  part  of  the  mechanism  is  injured,  is  evidenced 
by  the  appearance  of  albumin  in  the  urine  that  is  subse- 
quently first  secreted. 

Diuretics  are  substances  which  increase  the  flow  of 
urine ;  one  class,  known  as  saline  diuretics,  do  this  by 
bringing  about  hydremic  plethora,  and  by  causing  a 
dilatation  of  the  renal  arterioles.  Amongst  the  saline 
diuretics  are  sodium  chlorid,  urea,  dextrose,  sodium  ace- 
tate, and  many  others.  On  injecting  any  of  these  into 
the  blood,  the  first  effect  is  a  rise  in  the  osmotic  pressure 
of  the  plasma,  the  rise  being  proportionate  to  the  result- 
ing increase  in  molecular  concentration.  This  increase 
of  osmotic  pressure  causes  the  absorption  of  water  from 
the  lymph-spaces,  and  the  blood  will  be  diluted  ;  we 
shall  have  a  condition  of  hydremic  plethora.  The  bulk 
of  the  blood  being  thus  increased,  the  pressure  within 
the  vessels  is  raised,  consequently  the  filtration  of  urine 
will  be  hastened.  Even  when  the  condition  of  plethora 
has  disappeared  diuresis  may  continue,  for  tKe  renal  arte- 
rioles remain  dilated  for  some  time.  That  the  saline 
diuretics  do  not  act  through  stimulation  of  the  epithe- 
lium is  proved  by  the  fact  that  they  produce  no  diuresis 
if,  on  their  administration,  an  increased  blood  supply  to 
the  kidney  is  prevented.  The  dilatation  of  the  renal 
arterioles  is  caused  by  a  direct  action  of  these  diuretics 
either  on  the  walls  of  the  vessels  or  on  the  peripheral 
nervous  mechanism.  The  existence  of  secretory  nerve- 
fibers  for  the  kidney  has  not  been  proved. 

The  urine  is  carried  from  the  kidney  to  the  bladder 
through  the  ureter,  its  passage  being  aided  by  rhythmic 


134  EXCRETION. 

contractions  which  sweep  down  the  ureter  every  twenty 
seconds  or  so.  These  appear  to  be  of  muscular  origin, 
since  they  may  continue,  after  isolation,  in  the  portions 
of  the  ureter  which  contain  no  nerve-cells.  The  ureter, 
on  reaching  the  bladder,  runs  for  a  short  distance 
obliquely  through  the  bladder-wall ;  a  valve  is  thus 
formed  which  prevents  the  backflow  of  urine  from  the 
bladder  into  the  ureter,  for  a  rise  of  pressure  in  the 
former  will  compress  this  portion  of  the  latter. 

Micturition. — When  the  bladder  contains  no  urine, 
its  muscular  walls  are  in  a  state  of  slight  tonic  contrac- 
tion ;  as  urine  enters,  the  muscles  relax  slightly,  and, 
provided  the  urine  is  not  introduced  too  rapidly,  allow 
an  accumulation  of  about  250  c.c. ;  when  this  point  has 
been  reached,  rhythmic  contractions  appear  and  increase 
in  force  as  distention  goes  on.  The  exit  of  the  urine 
into  the  urethra  is  prevented  by  the  elasticity  of  the 
neck  of  the  bladder  and  of  the  surrounding  parts,  and, 
almost  surely,  by  a  reflex  tonic  contraction  of  the  cir- 
cular coat  of  muscle  at  this  point.  As  the  bladder  fills 
a  desire  to  urinate  is  felt.  The  emptying  of  the  bladder 
may  perhaps  be  instituted  by  a  voluntary  inhibition  of 
the  center  which  exerts  a  tonic  control  over  the  circular 
layer  of  muscle  surrounding  the  neck  of  the  bladder ; 
at  the  same  time,  a  voluntary  contraction  of  the  abdo- 
minal muscles  raises  the  intravesical  pressure,  and 
assists  in  the  expulsion  of  the  urine.  The  chief 
factor  in  expelling  the  urine  is,  however,  the  reflex 
contraction  of  the  muscular  wall  of  the  bladder 
itself.  The  exit  of  urine  may  be  prevented  or  retarded 
by  a  voluntary  contraction  of  the  perineal  muscles. 
After  division  of  the  spinal  cord  in  the  thoracic  region, 
micturition  may  be  carried  on  reflexly  by  centers 
situated  in  the  lumbar  cord.  The  bladder  is  innervated 
through  two  sets  of  nerves  ;  one  set,  leaving  the  lumbar 


SECRETION  OF  SWEAT.  135 

region,  enters  the  sympathetic,  and,  reaching  the  in- 
ferior mesenteric  ganglia,  is  here  connected  with  gan- 
glion cells  from  which  originate  post-ganglion ic  fibers; 
these  are  distributed  to  the  bladder  through  the  hypo- 
irnstric  nerve  and  plexus.  Stimulation  of  these  nerves 
excites  weak  contractions  of  the  bladder- wall,  but 
M.metimes  the  result  is  an  inhibition  of  these  muscles. 
The  other  set  of  fibers  leaves  the  cord  in  the  sacral 
nerves,  and,  without  entering  the  sympathetic,  reaches 
the  hyj>ogastric  plexus  through  the  nervi  erigentes. 
These  fibers  end  in  small  ganglia,  situated  in  or  near 
the  bladder-wall^  where  they  come  into  contact  relations 
with  the  cells  whose  axons  form  the  post-ganglion  ic 
link  in  this  chain.  These  nerves,  when  stimulated, 
cause  strong  contractions  of  the  bladder  and  expulsion 
of  the  urine.  If  the  lumbar  region  of  the  spinal  cord 
is  destroyed,  all  nervous  control  over  the  bladder  is 
lost,  but,  in  the  dog,  the  bladder  empties  itself  at  irregu- 
lar intervals,  a  stimulus  being  afforded  to  the  muscle  by 
the  stretching  which  results  from  distention  ;  in  man, 
the  urine  accumulates  in  the  bladder  to  a  certain  extent, 
and,  after  this,  as  the  urine  enters  from  the  ureters,  the 
excess  drains  off  through  the  urethra. 

Secretion  of  Sweat. — The  sweat  is  a' watery  fluid 
containing  but  a  small  percentage  of  solid  matter. 
Sodium  chlorid  forms  the  chief  solid  constituent ;  there 
are  also  present  other  salts,  fatty  acids,  and  traces  of 
urea.  The  sweat  is  ordinarily  acid  in  reaction  ;  but  if 
abundant,  is  neutral  or  alkaline.  In  uremia  the  amount 
of  urea  is  sometimes  much  increased.  The  amount  of 
sweat  secreted  naturally  varies  considerably,  being  much 
greater  in  warm  than  in  cold  weather.  Ordinarily,  the 
sweat  evaporates  as  fast  as  it  reaches  the  surface ;  this 
is  called  invisible  or  insensible  perspiration.  The 
amount  of  insensible  perspiration  depends  upon  the 


136  EXCRETION. 

condition  of  the  surrounding  atmosphere  ;  if  the  air  be 
moist,  less  of  the  sweat  will  evaporate  and  the  skin 
will  be  visibly  damp ;  if  the  air  be  dry  and  warm, 
evaporation  will  go  on  more  rapidly  and  the  skin  may 
appear  dry,  though  the  secretion  may  in  reality  be 
more  abundant.  When  the  skin  is  flushed,  the  secre- 
tion of  sweat  is  usually,  but  not  necessarily,  increased. 
An  abundant  supply  of  blood  to  the  sweat  glands  favors, 
but  does  not  provoke,  their  activity,  which  is  controlled 
by  definite  secretory  nerves.  These  nerve-fibers  leave 
the  thoracic  and  upper  lumbar  regions  of  the  spinal 
cord,  and  end  in  the  ganglia  of  the  lateral  sympathetic 
chain ;  the  post-ganglionic  fibers,  which  arise  from  cells 
in  these  ganglia,  pass  through  the  gray  rami  to  the 
various  spinal  nerve-trunks,  and  are  distributed,  through 
the  cutaneous  branches  of  these,  to  the  sweat  glands. 
The  course  is  similar  to  that  followed  by  the  vasocon- 
strictors. The  pre-ganglionic  sweat  nerves  for  the  skin 
of  the  face  and  head  end  in  the  superior  cervical 
sympathetic  ganglion.  It  is  not  known  whether  there 
exists  in  the  medulla  a  chief  sweat  center  to  which  the 
spinal  sweat  centers  are  subordinate.  As  is  well  known, 
sweat  may  be  secreted  as  a  result  of  the  emotions ;  in 
such  cases  the  spinal  centers  are  stimulated  by  invol- 
untary nerve  impulses  descending  from  the  brain  ;  they 
cannot  be  voluntarily  controlled.  The  secretion  of 
sweat  is  ordinarily  a  reflex  event  arising  from  the 
stimulation  of  afferent  cutaneous  nerves,  as  by  the 
application  of  heat.  That  it  is  not  a  result  of  the  direct 
stimulation  of  the  glands  by  heat  is  shown  by  the  fact 
that  exposure  to  heat,  after  the  division  of  the  nerves 
of  a  part,  does  not  cause  sweating  of  the  paralyzed 
area.  At  the  same  time,  the  impossibility  of  provoking 
the  secretion  by  increasing  the  blood  supply  is  demon- 
strated, for,  owing  to  the  division  of  the  vasoconstrictors, 


THE  SECRETION  OF  MILK.  137 

the  skin  will  be  flashed,  yet  it  will  remain  dry.  On 
the  other  hand,  stimulation  of  the  peripheral  end  of  the 
divided  nerve,  although  it  will  bring  about  a  paling  of 
the  skin,  through  the  stimulation  of  the  vasoconstrictors, 
will  cause  sweating  of  the  part  by  exciting  the  sweat 
nerves.  The  result  of  stimulating  the  renal  nerves  has 
an  entirely  different  effect  on  the  secretion  of  urine. 

The  sweat  centers  may  be  directly  stimulated  by  a 
rise  in  the  temperature  of  the  blood,  or  by  venous 
blood.  Atropin  prevents  the  secretion  of  sweat  by 
paralyzing  the  terminations  of  the  secretory  nerves  ; 
pilocarpin  causes  sweating  by  stimulating  either  the 
terminations  of  these  nerves  or  the  gland  cells  them- 
selves ;  it  possibly  acts  in  both  ways.  Strychnin  causes 
secretion  by  its  action  on  the  spinal  cord  ;  nicotin  acts 
chiefly  on  the  centers,  but  to  a  certain  extent  on  the 
peripheral  mechanism. 

The  sebaceous  glands  of  the  skin  have  not  been 
shown  to  be  controlled  through  the  nerves.  The  sebum 
excreted  by  these  glands  consists  of  the  debris  which 
results  from  the  degeneration  of  the  epithelial  cells  of 
the  glands  themselves.  It  is  an  oily  liquid  made  up 
of  fats,  fatty  acids,  cholesterin,  proteid,  ,  salts,  and 
water. 

The  ill  effects  of  coating  the  skin  with  varnish  are 
not  due  to  interference  with  excretion  through  the  cuta- 
neous glands,  but  to  the  resulting  dilatation  of  the  cuta- 
neous vessels  and  consequent  loss  of  heat. 

The  Secretion  of  Milk. — Unlike  the  sebaceous  and 
sweat  glands,  to  which  it  is  nearly  related,  the  mam- 
mary gland  is  only  occasionally  active ;  in  the  male, 
with  very  infrequent  exceptions,  never.  That  the 
activity  of  this  gland  may,  to  a  certain  extent,  be  in- 
fluenced by  the  nervous  system  is  proved  by  the  fre- 
quent instances  of  the  cessation  or  modification  of  lae- 


138  EXCRETION. 

tation  as  a  result  of  emotions  or  nervous  disorder. 
There  is,  however,  little  or  no  experimental  evidence 
from  which  we  can  gain  an  insight  into  the  mechanism. 
Milk  consists  chiefly  of  water,  holding  in  solution  pro- 
teids,  carbohydrates,  and  inorganic  salts ;  and  in  sus- 
pension, globules  of  fat.  The  chief  proteid,  or  nucleo- 
albumin,  is  caseinogen  ;  in  addition,  there  are  smaller 
quantities  of  albumin  and  globulin.  Lactose  is  the 
chief  carbohydrate,  and  occurs  in  larger  amount  than 
the  caseinogen.  The  fat  consists  of  stearin,  palmitin, 
olein,  and  smaller  quantities  of  other  fats.  The  inor- 
ganic constituents,  with  the  exception  of  iron,  closely 
correspond,  in  the  proportion  which  they  bear  to  one 
another,  to  those  of  the  new-born  animal. 

The  average  proportions  of  the  constituents  of  nor- 
mal human  milk  and  cows'  milk  are  as  follows  : 

HUMAN.  Cows'. 

Fat 4.   %  4.      % 

Sugar 7.    %  4.5   % 

Proteids  ....    1.5^  3.5   % 

Salts 0.2^  0.75% 

Water 87. 3  #  87.25^ 

Before  lactation  begins  the  alveoli  of  the  gland  en- 
large, the  epithelium  thickens,  and  the  cells  multiply. 
There  appear  within  the  cells,  more  particularly  near 
their  free  border,  granules  and  fat  droplets  which  are 
extruded  into  the  alveoli.  At  the  beginning  of  lacta- 
tion for  a  day  or  two  the  secretion  varies  from  that 
which  follows,  in  having  numerous  degenerated  cells,  a 
lower  percentage  of  fat  and  sugar,  and  almost  four 
times  as  much  proteid.  The  effect  of  this  early  secre- 
tion, which  is  called  colostrum,  is  to  cause  a  free 
evacuation  of  the  bowels  of  the  nursing  child.  Colos- 
trum is  lacking  in  caseinogen,  in  spite  of  its  high  pro- 
teid percentage. 

The  normal  physiological  stimulus  to  the  activity  of 


QUESTIONS.  139 

the  n-land  cells  is  (he  emptying  of  the  ducts,  and  al- 
though iij)  to  a  certain  point  the  secretion  is  continuous 
without  external  stimulus,  when  the  alveoli  and  ducts 
arc  distended  secretion  is  inhibited  reflex  ly  or  directly 
liv  the  high  pressure  in  the  ducts,  to  be  resumed,  and 
at  a  very  rapid  rate,  when  the  child  nurses.  The  ac- 
tivity of  the  gland  varies  with  the  physical  stimulus  of 
the  sucking  child.  The  amount  varies  under  normal 
conditions  from  10  to  1(5  ounces  a  day  in  the  first  week 
of  lactation,  to  30  to  40  ounces  a  day  in  the  ninth  month 
of  lactation. 

In  an  average  nursing  period  of  ten  to  twenty  min- 
utes, the  amount  obtained  from  a  single  breast  varies 
from  about  one  ounce  in  the  first  week  to  six  ounces  in 
the  sixth  week  and  later.  Lactation  usually  ceases 
promptly  when  nursing  is  discontinued,  but  the  appli- 
cation of  pressure  and  cold,  and  the  use  of  atropin 
and  saline  cathartics  hasten  the  cessation  of  the  glandu- 
lar activity,  and  the  process  of  involution  in  the  gland. 

The  proteids  of  the  diet  if  in  excess  increase  the  pro- 
teid  caseinogen  of  the  milk,  also  the  fat  and  possibly 
the  sugar.  Lack  of  exercise  will  have  the  same  effect 
as  excessive  proteid  diet.  The  percentage />f  fats,  car- 
bohydrates, and  proteids  in  the  milk  can  be  easily 
diminished  by  a  free  fluid  diet. 

QUESTIONS  FOR  CHAPTER  VI. 

What  are  the  most  prominent  differences  between  the  composi- 
tion of  the  blood  plasma  and  that  of  the  urine? 

What  readily  diffusible  sul>stance  is  found  in  the  blood,  but  not 
in  the  urine? 

What  nondiffusible  substance,  when  it  is  introduced  into  the 
blood,  appears  in  the  urine? 

Carefully  compare  the  effect  of  dividing  the  renal  nerves,  with 
that  of  stimulating  them,  (a)  in  regard  to  the  renal  blood  supply, 
and  (6)  with  respect  to  the  secretion  of  urine? 


140  EXCRETION. 

Make  a  similar  comparison  of  the  effects  of  dividing  and  stimu- 
lating the  sciatic  nerve  on  the  blood  supply  and  activity  of  the 
sweat  glands  of  the  leg  ? 

Compare  the  nature  of  the  control  exercised  by  the  nervous  sys- 
tem, on  the  one  hand,  over  the  secretion  of  urine,  on  the  other, 
over  the  secretion  of  sweat  ? 

Under  what  circumstances  may  the  quantity  of  urine  in  health 
fall  considerably  below  the  average  ? 

What  effect  have  the  seasons  on  the  specific  gravity  of  the  urine  ? 

How  do  you  collect  twenty-four  hours'  urine  ? 

Why  does  the  injection  of  a  large  quantity  of  normal  saline  so- 
lution into  the  vessels  cause  diuresis  ? 

Supposing  that  the  sodium  chlorid  of  the  plasma  were  incapable 
of  passing  from  the  glomerulus  into  the  capsule,  would  the  blood 
pressure  required  for  the  filtration  of  water  be  greater  or  less  than 
the  normal  ? 

•    How  do  you  account  for  the  fact  that  the  urine  is,  in  respect  to 
inorganic  constituents,  more  concentrated  than  the  plasma  ? 

Would  you  expect  the  reaction  of  the  urine  to  vary  with  its 
specific  gravity  ?  Why  ? 

What  effect  has  the  administration  of  alkalies  on  the  relations 
existing  between  different  nitrogenous  compounds  of  the  urine  ? 

What  is  the  simplest  method  of  producing  diuresis  ? 

Which  of  the  normal  constituents  of  the  blood  plasma,  when 
present  in  excess,  cause  diuresis  ? 

How  would  the  secretion  of  urine  be  affected  by  increasing  the 
percentage  of  proteids  in  the  blood  plasma  ? 

How  may  the  reaction  of  the  urine  be  caused  to  resemble  that 
of  the  blood  ? 

How  does  starvation  modify  the  urine  of  the  herbivora  ? 

What  relation  exists  between  the  amount  of  blood  supplied  to 
the  kidney  and  the  reaction  of  the  urine  ? 

How  may  we  determine  whether  a  drug  which  exerts  an  influ- 
ence over  the  secretion  of  sweat  acts  upon  the  sweat  centers  or  on 
the  peripheral  mechanism  ? 

How  may  we  determine  whether,  on  application  of  heat  to  the 
skin,  the  sweat  glands  are  stimulated  directly  or  reflexly  ? 

What  are  the  reasons  for  the  intermittent  function  of  the  mam- 
mary glands? 

Describe  the  normal  course  of  lactation. 


CHAPTER  VII. 
ANIMAL  HEAT. 

THE  temperature  of  the  body  depends  upon  the  liber- 
ation, in  the  form  of  heat,  of  the  potential  energy  in- 
troduced in  food.  This  is  set  free,  not  only  from  the 
food  that  has  been  absorbed  and  assimilated,  but  to  a 
l«-ss  extent  from  the  food  as  it  undergoes  digestion  in 
the  alimentary  canal.  The  larger  proportion  of  heat  is 
produced  in  the  muscles,  the  process  being  under  the 
control  of  the  central  nervous  system.  Next  to  the 
muscles  in  heat  production  come  the  glands,  more 
especially  the  liver.  In  order  that  the  temperature  may 
remain  constant,  as  it  does  within  very  narrow  limits, 
exactly  the  same  amount  of  heat  must  be  liberated 
within  the  body  as  is  given  off  from  the  surface  and  lost 
in  the  excreta.  If  the  production  of  heat  fails  to  keep 
pace  with  the  loss,  the  temperature  sinks ;  if  the  pro- 
duction of  heat  is  more  rapid  than  the  loss,  the  tempera- 
turc  goes  up.  Both  production  and  loss  are  very  vari- 
al>le,  but  in  the  normal  condition  the  one  keeps  pace 
with  the  other.  In  fever,  if  the  temperature  remains 
constant,  the  same  is  true  ;  but  in  this  case  the  adjust- 
ment fails  during  the  rise  of  temperature. 

If  a  cold-blooded,  or  poikilothermic,  animal  is  ex- 
posed to  cold,  its  temperature  sinks  to  that  of  its  sur- 
roundings ;  on  exposure  to  heat  its  temperature  rises. 
Wurm-blooded,  or  homoiothermic,  animals  behave  quite 
otherwise ;  for  instance,  a  dog  was  placed  in  a  chamber 

141 


142  ANIMAL  HEAT. 

the  temperature  of  which  was  — 91°  C.  ( — 130°  F.) ; 
the  first  effect  was  a  slight  rise  in  the  dog's  tempera- 
ture. 

The  metabolism  of  the  muscles  is  governed  by  the 
central  nervous  system,  and  the  cells  of  the  nervous 
system  are  subjected  to  afferent  impulses  coming  from 
the  periphery  ;  for  instance,  from  the  skin.  If  cold  be 
applied  to  the  skin,  it  stimulates  certain  afferent  nerves, 
which  in  turn  transmit  impulses  to  the  central  nervous  ; 
system,  and  cause  the  dispatch  of  efferent  nerve  im- 
pulses which  hasten  the  chemical  changes  within  the 
muscles ;  more  material  is  oxidized  within  the  muscle, 
and  more  heat  is  produced.  If  the  cold  be  at  all  in- 
tense, the  increased  metabolism  of  the  muscle  will  find 
visible  expression  in  shivering,  which  consists  of  weak 
incoordinated  contractions.  The  value  of  shivering  is 
apparent.  At  the  same  time  there  occurs  a  reflex  con- 
striction of  the  cutaneous  arterioles,  brought  about  by 
the  stimulation  of  the  vasoconstrictor  center  through  the 
afferent  nerves  of  the  skin.  In  consequence  of  this  con- 
striction, less  blood  will  flow  through  the  superficial 
vessels,  and  the  loss  of  heat  will  be  much  less  than  it 
would  be  were  more  blood  brought  near  the  surface. 
The  animal  will  feel  cold,  owing  to  the  cooling  of  the 
surface  and  peripheral  terminations  of  the  sensory  nerves, 
which  carry  impulses  toward  the  brain,  but  its  temper- 
ature may,  in  reality,  be  a  little  higher  than  usual. 
Amongst  the  afferent  nerves  of  the  skin  are  two  sets  of 
fibers  whose  peripheral  terminations  are  so  specialized 
that  they  are  stimulated  by  slight  changes  of  tempera- 
ture. One  set  is  stimulated  by  cooling,  and  transmits 
impulses  which,  on  reaching  the  brain,  give  rise  to  a  sen- 
sation of  cold ;  they  are  unaffected  by  warmth.  The 
other  set  is  stimulated  by  a  rise  of  temperature,  the  re- 
•  suiting  sensation  being  one  of  heat.  Whether  the  reflex 


THEKMOGENIC  CENTERS.  1  I:: 

effects  of  changes  of  temperature  are  produced  through 
the-e  nerves  is  uncertain,  but  highly  probable. 

The  metabolism  of  the  muscles  is  controlled  by  nerve- 
cells  H  mated  in  the  spinal  cord,  and  these  have  been 
called  thermogenic  centers;  there  is  no  reason  to  sup- 
pose that  these  cells  are  other  than  the  ordinary  motor 
nerve  cells  which  govern  the  contraction  of  the  muscles. 
They  do  not  appear,  in  the  absence  of  higher  centers,  to 
afford  a  mechanism  which,  on  exposure  to  cold,  suffices 
for  the  regulation  of  the  temperature,  through  increased 
production  of  heat;  for  the  animal  whose  spinal  cord 
IIMS  been  divided  in  the  cervical  region  behaves  as  a 
cold-blooded  animal ;  its  metabolism  is  depressed  by  ex- 
po i ire  to  cold,  increased  by  exposure  to  heat.  The 
activity  of  the  thermogenic  centers  of  the  cord  appeal's 
to  be  regulated  by  centers  situated  in  some  higher 
portion  of  the  central  nervous  system,  these  latter 
centers  being  influenced  by  the  afferent  impulses  which 
are  inaugurated  by  changes  in  the  temperature  of  the 
surroundings. 

A  warm-blooded  animal  may  be  exposed  to  great 
heat  and  yet  maintain  a  constant  body-temperature. 
This  is  due,  not  so  much  to  a  lessened  production  of  heat, 
as  to  an  increased  loss  of  heat  from  the  surface.  The 
application  of  warmth  to  the  skin  brings  about  a  reflex 
dilatation  of  the  cutaneous  vessels ;  the  skin  flushes,  more 
blood  being  brought  near  to  the  surface.  If,  however, 
the  temperature  of  the  surrounding  atmosphere  be  much 
greater  than  that  of  the  body,  the  effect  of  this  event, 
taken  by  itself,  would  be  a  rise  of  body-temperature,  for 
heat  would  be  transmitted  from  the  air  to  the  blood. 
This,  in  the  normal  condition,  does  not  happen,  unless 
the  heat  be  intense  or  the  exposure  l>e  prolonged.  We 
have  already  seen  that  the  application  of  heat  to  the 
skin  causes  a  reflex  secretion  of  sweat ;  in  the  evapo- 


144  ANIMAL  HEAT. 

ration  of  this  sweat,  a  large  quantity  of  heat  is  absorbed 
from  the  blood  and  carried  off,  as  latent  heat,  in  the  re- 
sulting watery  vapor.  This  is  the  most  potent  factor  in 
preventing  a  rise  of  body-temperature  on  exposure  to  a 
warm  atmosphere.  It  will  be  readily  understood  that 
the  cooling  of  the  skin  in  this  way  will  be  materially  in- 
fluenced by  the  state  of  the  surrounding  air.  If  the  air 
be  dry,  evaporation  will  be  favored ;  if  moist,  retarded. 
The  effect  of  a  hot  bath  is  to  raise  the  temperature  of 
the  body,  for  water  is  a  much  better  conductor  than  air, 
and  if  warmer  than  the  blood,  will  rapidly  give  up  heat 
to  the  latter ;  at  the  same  time,  evaporation  from  the  ' 
immersed  skin  will  be  prevented.  A  bath  in  water  at 
45°  C.  would  soon  prove  fatal,  wrhile  exposure  to  dry 
air  at  125°  C.  might  be  borne  with  impunity  for  the 
same  length  of  time.  The  first  effect  of  a  warm  bath  is 
a  slight  rise  of  body-temperature  ;  after  the  bath  is  over 
there  is  a  slight  fall,  but  a  return  to  normal  soon  follows. 
Although  a  cold  bath  abstracts  much  heat  from  the 
body,  the  metabolism  is  so  stirred  up  that  the  first  effect 
may  be  a  slight  rise  of  body-temperature ;  if  the  bath 
be  prolonged,  a  slight  fall  may  result,  but  on  leaving 
the  water  the  temperature  rises  a  little  above  normal. 
An  animal  which  possesses  much  subcutaneous  fat  is 
better  protected  from  a  loss  of  heat  than  one  that  is  lean. 
The  involuntary  regulation  of  the  body-temperature  may 
be  voluntarily  assisted  by  the  donning  or  doffing  of 
clothing,  and  by  taking  or  abstaining  from  exercise. 
The  average  axillary  temperature  is  about  37.1°(98.8a 
F.).  Small  daily  variations  occur,  the  temperature 
being '  lowest  between  midnight  and  early  morning, 
highest  in  the  late  afternoon  ;  the  effect  of  a  meal  is  to 
slightly  raise  the  temperature.  If  a  warm-blooded 
animal  is  exposed  to  such  intense  cold  that  the  height- 
ened metabolism  cannot  keep  pace  with  the  great  loss 


QUESTIONS.  145 

from  the  surface,  the  temperature,  after  the  preliminary 
rise,  gradually  sinks ;  unconsciousness  supervenes,  and 
is  followed  by  death.  The  hibernating  animals  with- 
stand the  fall  of  body-temperature,  which  may  go  almost 
as  far  as  0°  C.,  without  ill  effects.  Metabolism  pru- 
<  <  < ds  at  a  minimal  rate  ;  the  heart-beat  is  weak  and  in- 
fre<|iient;  respiration  is  depressed  and  irregular,  and 
the  respiratory  exchange  almost  ceases.  The  respiratory 
<|iii>tient  sinks,  for  oxygen  may  be  stored  in  the  body; 
the  animal  may,  in  this  way,  gain  slightly  in  weight, 
('old-blooded  animals  may  be  frozen  solid,  and  by 
gradual  thawing  be  resuscitated;  a  snail  has  been  re- 
< lured  to  a  temperature  of — 1 20°  C.  without  succumbing. 
In  this  case  metabolism,  of  course,  ceases;  life  becomes 
latent. 

Changes  of  temperature  affect  proteid  metabolism 
verv  little ;  the  increased  production  of  heat  which 
c -n. -nes  on  exposure  to  cold  is  accomplished  at  the  ex- 
pense of  the  non nitrogenous  foods. 

A  warm-blooded  animal  poisoned  with  curari  reacts 
to  changes  of  temperature  as  though  it  were  cold 
blooded.  Curari  paralyzes  the  terminations  of  the 
motor  nerve-fibers,  and  thus  deprives  the  Central  nerv- 
ous system  of  its  control  over  the  chief  thermogenic 
tissue  of  the  body. 

QUESTIONS  FOR  CHAPTER  VII. 

If  heat  is  being  continually  produced  within  the  body,  why  does 
not  the  temperature  of  the  body  continually  rise? 

What  nervous  centers  are  concerned  in  regulating  the  loss  of 
heat? 

Does  the  activity  of  these  centers  usually  vary  in  the  same  direc- 
tion? 

In  what  respects  is  the  regulation  of  body-temperature  affected 
by  a  division  of  the  afferent  cutaneous  nerves  ? 
10 


146  ANIMAL  HEAT. 

After  this  operation,  will  an  animal  better  withstand  exposure 
to  heat  or  cold  ? 

Compare  the  effect  on  the  regulation  of  body-temperature  which 
results  from  division  of  the  ventral  spinal  nerve-roots  with  that 
which  follows  division  of  the  sympathetic  rami  communicantes.  In 
the  former  case,  what  reflex  which  normally  follows  exposure  to  cold 
will  be  prevented,  while  in  the  latter  case  it  persists  ?  What  cold 
and  heat  reflexes  will  be  rendered  impossible  in  each  case  ? 

In  very  hot  weather,  will  the  administration  of  atropin  tend 
to  raise  or  lower  the  body-temperature  ? 

Can  we  by  means  of  the  clinical  thermometer  determine  the 
rate  of  heat  production  or  heat  loss  ? 

Under  what  circumstances  may  the  temperature  of  the  body  rise, 
while  the  production  of  heat  remains  constant  ? 

Does  a  fall  of  body-temperature  always  depend  on  lessened  heat 
production  ? 

The  sensation  of  warmth  which  on  a  cold  day  results  from  drink- 
ing alcohol  is  due  to  the  warming  of  the  skin  by  an  increase  in  the 
cutaneous  circulation,  the  activity  of  the  constrictor  center  being 
depressed  by  the  alcohol.  What  is  the  effect  on  the  temperature  of 
the  body  as  a  whole  ? 


CHAPTER  VIII. 
MUSCLE  AND  NERVE. 

THE  physiology  of  muscle  and  nerve  is  best  and  most 
profitably  studied  in  the  laboratory  ;  only  a  mere  outline 
of  the  subject  need  be  given  here. 

The  general  properties  of  skeletal,  cardiac,  and  plain 
muscle  are  the  same,  but  display  minor  differences. 
Skeletal  muscles  may  be  controlled  by  the  will,  but  are 
also  subject  to  reflex  influences.  The  contraction  of 
cardiac  muscle  is  independent  of,  but  regulated  by,  the 
nervous  system.  Plain  muscle,  with  the  exception  of 
the  ciliary  muscle,  is  beyond  the  control  of  the  will ;  its 
contraction  is  ordinarily  reflex,  but  if  it  be  deprived  of 
nervous  influence,  it  may  develop  an  independent  tone. 
The  ease  with  which  chemical  changes  may  be  set  going 
within  normal  muscle  renders  it  irritable ;  that  is,  it  is 
capable  of  responding  to  a  stimulus.  Cardiac  muscle  is 
more  irritable  than  plain  muscle;  plain  muscle  than  skel- 
etal. Muscle  responds  to  mechanical,  thermal,  chemical, 
and  electrical  stimuli,  and  to  the  normal  nerve  impulse 
the  nature  of  which  has  not  been  determined.  In  order 
that  the  application  of  a  force  may  act  as  a  stimulus  it 
must  be  of  sufficient  intensity  and  duration,  and  must  not 
be  too  gradual.  On  the  application  of  a  stimulus,  a  mus- 
cle shortens  and  thickens  without  changing  its  bulk ; 
this  is  called  contraction.  That  muscle  is  directly  irri- 
table may  be  shown  by  paralyzing  the  terminations  of 

147 


148  MUSCLE  AND  NERVE. 

its  motor  nerve  with  curari ;  in  this  condition  it  is  still 
responsive  to  a  stimulus. 

Muscle  is 'extensible,  but  does  not  stretch  in  propor- 
tion to  the  force  applied;  as  the  elongation  is  increased, 
the  extensibility  becomes  less  and  less.  On  cessation 
of  stretching,  or  other  distortion,  muscle,  by  virtue  of 
its  elasticity,  resumes  its  normal  shape. 

When  a  muscle  is  stimulated  it  contracts,  but  there 
is  a  momentary  delay  in  the  appearance  of  the  mechan- 
ical change ;  this  is  known  as  the  latent  period  of  mus- 
cle. When  the  stimulation  is  direct,  the  latent  period 
amounts  to  about  0.004  second ;  if  the  muscle  be  indi- 
rectly stimulated,  by  applying  the  excitant  to  its  nerve, 
the  latent  period  is  prolonged  to  about  0.007  second, 
the  extra  delay  being  due  to  the  motor  end-plate ;  in 
addition  to  this,  the  time  which  elapses  between  the 
stimulation  of  a  nerve  and  the  beginning  of  the  mechan- 
ical response  of  the  muscle  will  be  influenced  by  the 
length  of  nerve  over  which  the  nerve  impulse  has  to 
travel.  The  average  rate  of  transmission  of  the  nerve 
impulse  is  about  50  meters  per  second.  The  contrac- 
tion produced  by  a  single  induction  shock  lasts  about 
0.1  second,  but  varies  with  the  resistance  offered  and 
with  the  condition  of  the  muscle.  The  contraction  of 
plain  muscle  is  very  much  more  prolonged.  The  con- 
traction of  muscle  may  be  divided  into  the  period  of 
shortening  and  the  period  of  relaxation,  the  former  being 
of  somewhat  less  duration  than  the  latter.  The  con- 
traction of  a  muscle-fiber  is  not  confined  to  the  point 
stimulated,  but  sweeps  over  the  whole  fiber,  as  a  wave, 
with  a  velocity  of,  in  human  muscle,  about  10  meters 
per  second. 

The  extent  of  shortening  varies  with  the  condition  of 
the  muscle,  the  strength  of  stimulus,  the  weight  lifted, 


FATIGUE.  149 

the  way  in  which  the  weight  is  applied,  etc.  Other 
conditions  remaining  the  same,  the  degree  of  shortening 
is  less  in  a  fatigued  than  in  a  fresh  muscle ;  the  short- 
ening occurs  rather  more  slowly ;  the  relaxation  is  very 
much  prolonged.  Fatigue  depends  on  several  factors ; 
it  is  due  in  part  to  the  consumption  of  the  store  of 
energy-containing  material,  in  part  to  the  accumulation 
of  waste  products.  The  motor  nerve-ending  is  more 
sensitive  to  fatigue  than  the  muscle  itself.  The  cells 
of  the  central  nervous  system  concerned  in  producing 
muscular  contraction  are  also  subject  to  fatigue.  Con- 
traction is  much  prolonged  by  veratrin  and  by  adrenal 
extract.  If,  beginning  with  a  current  too  weak  to  pro- 
voke contraction,  successive  single  induction  shocks  of 
gradually  increasing  strength  be  passed  through  a  mus- 
cle, a  point  will  be  reached  where  a  just  visible  contrac- 
tion results ;  this  is  known  as  a  minimal  stimulus.  On 
further  increasing  the  strength  of  stimulus,  the  extent 
of  shortening  will  go  on  increasing  up  to  a  certain  j)oint, 
when  the  maximal  contraction  of  which  the  muscle  is 
capable  will  have  been  reached.  Further  increase  of 
stimulus  will  not  increase  the  extent  of  shortening.  If, 
however,  the  muscle  be  stimulated  at  short  intervals, 
with  a  stimulus  that  is  just  sufficient  to  cause  a  maxi- 
mal contraction  when  the  muscle  is  fresh,  until  it  shows 
signs  of  fatigue,  a  further  increase  in  the  strength  of 
the  stimulus  may  now  provoke  a  contraction  equal  to 
that  of  the  fresh  muscle. 

Cardiac  muscle  responds  to  even  a  minimal  stimulus 
with  a  maximal  contraction. 

If  a  muscle  be  caused  to  lift  a  load,  any  addition  of 
weight  will  reduce  the  height  to  which  the  load  is  lifted, 
though  it  does  not  necessarily  diminish  the  amount  of 
work  done.  The  work  accomplished  is  the  product  of 


150  MUSCLE  AND  NERVE. 

the  load  by  the  height  to  which  it  is  raised.  If  the 
muscle  contracts  without  lifting  a  load,  no  external 
work  is  done ;  the  energy  resulting  from  the  chemical 
change,  upon  which  contraction  depends,  is  all  liberated 
as  heat.  If  so  great  a  resistance  is  opposed  to  the  active 
muscle  that  it  cannot  shorten,  no  work  is  done,  the 
energy  set  free  all  appearing  in  the  form  of  heat.  When 
the  muscle  is  working  to  best  advantage,  not  more  than 
one-fourth  of  the  energy  set  free  is  converted  into  work, 
and  it  is  quite  possible  that  even  this  one-fourth  is  first 
set  free  as  heat  which,  by  causing  the  anisotropic  fibrillse 
to  absorb  water,  brings  about  their  shortening. 

The  efficiency  of  all  three  kinds  of  muscle  is  greatest 
when  they  contract  against  a  certain  amount  of  resistance. 

The  term  isometric  contraction  is  applied  to  a 
muscle  contraction  made  when  the  muscle  is  so  fixed  at 
both  ends  that  it  cannot  shorten  during  contraction. 

The  term  isotonic  contraction  is  applied  to  a  muscle 
contraction  made  under  such  conditions  that  the  tension 
of  the  muscle  remains  constant  throughout  the  contrac- 
tion. 

So  far  we  have  considered  only  the  single  contraction, 
or  twitch,  of  muscle.  In  the  body  it  is  comparatively 
seldom  that  a  muscle  contracts  for  so  short  a  period  as 
0.1  second  ;  usually  the  contraction  is  more  prolonged, 
and  probably  consists  in  the  fusion  of  a  number  of  sin- 
gle contractions,  which  are  provoked  by  successive  stim- 
uli following  each  other  so  rapidly  that  time  is  not 
allowed  for  relaxation.  If  the  voluntary  contraction  of 
muscle  be  graphically  recorded,  the  tracing  shows  a  slight 
rhythmic  oscillation  at  the  rate  of  about  10  to  12  per 
second,  which  appears  to  depend  on  the  dispatch,  by 
motor  nerve-cells  of  the  cord,  of  successive  nerve  im- 
pulses following  each  other  at  this  rate.  A  similar 
form  of  contraction  may  be  caused  by  artificial  stimula- 
tion of  muscle  with  rapidly  repeated  induction  shocks. 


IRRITABILITY.  151 

When  the  stimuli  arc  so  rapidly  repeated  that  a  graphic 
record  shows  no  undulations,  the  contraction  is  spoken 
of  as  complete  tetanus  ;  if  time  is  allowed  for  a  partial 
relaxation  between  contractions,  it  is  an  incomplete 
tetanus. 

The  breaking  induction  shock,  when  a  submaximal 
stimulus  is  used,  is  more  effective  than  the  making 
shock;  this  depends  on  the  induction  apparatus.  When 
the  voltaic,  constant,  or  battery  current  is  used,  closing 
the  circuit  (or  making  the  current)  is  more  effective  than 
opening  the  circuit  (or  breaking  the  current).  This  de- 
I tends  upon  changes  in  the  irritability  of  the  muscle,  or 
nerve,  as  the  case  may  be,  produced  by  the  passage  of 
the  current.  The  irritability  of  the  muscle  or  nerve  is 
raised  at,  and  in  the  neighborhood  of,  the  negative  elec- 
trode, or  kathode  ;  it  is  lowered  at  the  anode  and  in  its 
neighborhood.  It  is  supposed  that  a  sudden  rise  of  irri- 
ta  I  lility  serves  as  a  stimulus.  When  the  current  is  made, 
the  irritability  of  the  muscle  is  suddenly  raised  in  the 
neighborhood  of  the  kathode,  the  muscle  is  stimulated 
at  this  point,  and  a  contraction  instituted  which  travels 
along  the  muscle;  the  anodal  end  remains  relaxed  until 
this  wave  of  contraction  reaches  it.  The  "muscle  as  a 
whole  then  relaxes,  though  the  kathodal  end  maintains 
a  slight  degree  of  shortening.  This  continues  as  long 
as  the  current  flows  evenly ;  when  it  is  broken,  the  irri- 
tability of  the  anodal  end,  which  had  been  depressed 
below  the  normal,  suddenly  rises  to  normal  or  a  little 
above  it,  and,  if  the  current  be  of  sufficient  intensity,  a 
contraction  will  originate  at  this  point.  If  the  current 
be  weak,  no  contraction  will  result,  for  the  anodal  stim- 
ulus is  not  so  effective  as  the  kathodal.  The  relative 
efficiency  of  kathodal  and  anodal  stimuli  may  bear  some 
relation  to  the  fact  that,  in  the  case  of  the  former,  the 
rise  of  irritability  is  from  normal  upward,  while,  in  that 
of  the  latter,  it  is  a  return  to  normal  from  a  point  Mow 


152 


MUSCLE  AND  NERVE. 


it.  If  the  current  does  not  flow  evenly,  but  rises  or 
falls  in  intensity,  there  are  corresponding  changes  of 
irritability  in  the  muscle,  and  these  may  act  as  stimuli. 
If  a  nerve  which  is  connected  with  a  muscle  is  stim- 
ulated by  a  constant  current,  the  contraction  of  the 
muscle  will  depend  upon  the  direction  in  which  the 
current  flows,  and  upon  its  intensity.  What  happens 
is  shown  in  the  following  table,  which  illustrates  the 
so-called  law  of  contraction.  If,  when  a  current  is 
passed  through  a  nerve,  the  anode  is  nearest  the  muscle, 
it  is  called  an  ascending  current ;  if  the  kathode  is  next 
the  muscle,  a  descending  current. 

PFLUGER'S  LAW. 


CUKEENT  : 

Weak    

ASCENDING 

DESCENDING 

make 

C 
C 

break 

C 
C 

make 

C 
C 

C 

break 
C 

Medium 

Strong 

The  results  of  stimulation  with  weak  and  medium 
intensity  of  current  may  be  understood  from  what  has 
already  been  said,  but,  in  the  case  of  strong  stimulation, 
further  explanation  is  needed.  The  passage  of  a  con- 
stant current  not  only  modifies  the  irritability  of  a 
nerve,  it  also  changes  its  conductivity,  or  power  of 
transmitting  the  nerve  impulse.  With  weak  and  me-_ 
dium  currents,  the  change  in  conductivity  is  not  suffi- 
cient to  modify  the  result ;  but  with  strong  currents,  the 
eifect  is  pronounced.  While  a  strong  current  flows 
through  the  nerve,  the  conductivity  is  reduced,  not  only 
in  the  area  between  the  electrodes,  but  for  a  short  dis- 
tance on  either  side  of  them,  and  just  after  the  current 
ceases  to  flow  the  anodal  end  fails  to  transmit  the  im- 


CONDUCTIVITY.  153 


pulse,  With  a  strong  ascending  or  descending  current 
tin-  nerve  is  stimulated  on  making  the  current  at  the 
kathode;  on  breaking,  at  the  anode.  With  an  ascend- 
ing current,  however,  while  the  impulse  starting  at  the 
anode  easily  reaches  the  muscle,  the  impulse  which  re- 
sults from  making  the  current,  and  starts  from  the 
kathode,  is  by  the  lessened  conductivity  prevented  from 
passing  along  the  nerve,  and  no  contraction  ensues. 
( )n  the  other  hand,  with  a  descending  current  we  get  a 
making  contraction,  for  the  impulse  starts  from  the 
kathode  which  is  near  the  muscle,  while  the  impulse 
provoked  by  the  anodal  stimulus  fails  to  traverse  the 
anodal  area  of  depressed  conductivity,  and  we  get  no 
breaking  contraction.  The  condition  induced  in  a  nerve 
by  the  passage  of  a  constant  current  is  known  as  elec- 
trotonus  ;  that  at  the  anodal  end,  anelectrotonus  ;  at  the 
kathodal  end,  katelectrotonus.  In  order  to  stimulate  a 
nerve  in  the  intact  body,  one  electrode  is  usually  placed 
over  the  course  of  the  nerve,  the  other  on  some  indiffer- 
ent part  of  the  body,  at,  perhaps,  some  distance  from 
the  first.  Under  these  circumstances,  we  cannot  expect 
to  obtain  a  demonstration  of  the  law  of  contraction  just 
described,  for  the  current,  instead  of  being  confined  to 
the  nerve,  will  pass  obliquely  through  it  :  if  the  anode 
be  over  the  nerve,  in  a  sheaf  of  diverging  lines  ;  if  the 
kathode  be  over  the  nerve,  in  converging  lines.  In  the 
former  case  the  anelectrotonic  area  will  be  narrower 
than  the  katelectrotonic  area  ;  in  the  latter  case  the  con- 
ditions  will  be  reversed.  Where  the  lines  of  force  are 
the  more  concentrated,  the  current  will  be  denser  and 
its  effects  more  pronounced.  With  a  weak  current, 
therefore,  a  contraction  of  the  muscle  (which  is  inner- 
vated by  this  nerve)  will  be  most  readily  excited  by  the 
stronger  of  the  two  forms  of  stimulus,  the  making, 
when  the  area  of  katelectrotonus  is  concentrated  by 
placing  the  kathode  over  the  nerve.  With  an  intensity 


154 


MUSCLE  AND  NERVE. 


of  current  only  just  sufficient  to  give  this  result,  no 
contraction  can  be  obtained  on  breaking  the  current  if 
the  kathode  is  over  the  nerve  ;  no  contraction  occurs  at 
the  make  or  break  when  the  anode  is  over  the  nerve. 
If  we  now  increase  the  strength  of  the  current  little  by 
little,  and  use  first  one  electrode  and  then  the  other 
with  each  rise  in  intensity,  we  shall  reach  a  point  at 
which,  in  addition  to  the  result  already  obtained,  we 
get  making  and  breaking  contractions  when  the  anode 
is  over  the  nerve.  Of  these,  only  the  breaking  con- 
traction results  from  true  anodal  stimulation  ;  the  mak- 
ing contraction  results  from  stimulation  of  the  nerve  in 
the  katelectrotonic  area.  The  katelectro tonic  area  is 
more  diffuse  than  the  anelectrotonic  when  the  anode  is 
over  the  nerve,  but  the  greater  efficiency  of  the  katho- 
dal  stimulus  equalizes  the  effects  of  the  make  and 
break.  The  strength  of  the  current  must  be  still  fur- 
ther increased  before  we  can  obtain  a  breaking  con- 
traction with  the  kathode  over  the  nerve,  for  with  this 
arrangement  the  area  of  anelectrotonus  is  more  diffuse,  j 
The  results  thus  obtained  will  have  appeared  as  fol- 
lows : 

LAW  OF  UNIPOLAR  STIMULATION. 


CURRENT. 

ELECTRODE 
OVER  NERVE. 

CONTRACTION  ON  : 

ABBREVIATION. 

Minimal  .... 

kathode 

closing  circuit 

KCC. 

Medium 

kathode 
anode 

closing  circuit 
closing  circuit 

KCC. 
ACC 

anode 

opening  circuit 

AOC. 

Strong      ..... 

kathode 
anode 

closing  circuit 
closing  circuit 

KCC. 

ACC. 

anode 
kathode 

opening  circuit 
opening  circuit 

AOC. 
KOC. 

The  formula  for  this  normal  sequence  of  reactions  is 


CONDUCTIVITY.  155 

usually  written  thus,  KCC,  ACC,  AOC,  KOC,  and 
indicates  the  order  in  which  these  events  occur  with 
increasing  strength  of  current.  KCC  means  kathodal 
closing  contraction;  AOC,  anodal  opening  contraction, 
etc.,  closing  the  circuit  being  synonymous  with  making 
the  current ;  opening  the  circuit,  with  breaking  the 
current.  When  the  nerves  of  a  muscle  are  degenerat- 
ing, the  reaction,  for  some  reason,  varies  from  the 
normal,  the  anodal  closing  contraction  being  obtained 
with  a  weaker  current  than  the  kathodal  closing  con- 
traction ;  this  is  known  as  the  reaction  of  degeneration, 
and  affords  a  means  of  diagnosis.  Another  important 
means  of  determining  the  condition  of  a  muscle  de- 
pends upon  the  fact  that  after  the  degeneration  of  its 
nerves,  a  muscle  no  longer  responds  to  the  induced 
current,  while  its  irritability  to  the  constant  current 
rises  above  the  normal.  Its  irritability  should  be 
compared  with  that  of  the  corresponding  muscle  on  the 
opposite  side  of  the  body.  If  the  nerve  fails  to  regen- 
erate, the  muscle,  in  time,  undergoes  complete  atrophy. 

When  a  muscle  or  nerve  is  injured  at  a  certain 
point,  the  electric  potential  at  this  point  is  lo>vered ;  the 
injured  portion  becomes  negative  as  compared  with  the 
uninjured  portion.  If  the  injured  and  uninjured  parts 
be  connected  by  means  of  a  conductor, — a  wire,  for 
example, — a  current  will  flow  through  the  conductor 
IVmii  the  uninjured,  or  positive,  to  the  injured,  or 
negative,  pole  of  the  muscle.  This  is  called  the  cur- 
rent of  rest,  or  demarcation  current.  When  a  nerve 
has  been  divided  and  is  dropped  back  into  the  wound, 
the  surrounding  lymph  may  serve  to  connect  the  in- 
jured with  the  uninjured  portion  of  the  nerve,  a  cur- 
rent will  l)e  set  up,  and  the  nerve  may  l>e  stimulated ; 
this  must  be  taken  into  account  in  experimenting  upon 
divided  nerves. 

Not  only  is  an  injured  part  of  nerve  or  muscle  elec- 


156  MUSCLE  AND  NERVE. 

trically  negative  to  uninjured  parts,  but  active  parts  are 
negative  as  compared  with  resting  parts ;  consequently 
when  an  uninjured  portion  of  muscle  or  nerve  becomes 
active,  the  difference  of  potential  between  this  point 
and  an  injured  point  will  be  lessened,  and,  if  the  two 
points  are  connected  by  a  conductor,  the  demarcation 
current  will  be,  for  the  moment,  weakened;  this  weak- 
ening of  the  demarcation  current  is  called  the  negative 
variation. 

Every  nerve-fiber  is  an  outgrowth  from,  or  a  process 
of,  a  nerve-cell.  A  nerve-cell  usually  has  several  pro- 
cesses ;  one,  the  axis-cylinder  process,  or  axon,  becomes 
a  nerve-fiber ;  the  others  branch  freely  and  are  usually 
very  much  shorter  than  the  axon  ;  they  are  called  den= 
drites,  or  protoplasmic  processes.  A  nerve-cell  with 
its  processes  constitutes  a  neurone.  Each  process  is 
dependent  for  its  existence  upon  connection  with  the 
parent  nerve-cell ;  if  a  nerve-fiber  be  divided,  the  por- 
tion that  is  cut  off  from  the  cell  invariably  dies  ;  re- 
generation can  only  occur  through  the  growth  of  that 
portion  of  the  axon  which  remains  in  connection  with 
the  nerve-cell.  Division  of  the  axon  produces  secon- 
dary effects  on  the  cell  itself;  the  cell-body  shows  signs 
of  degeneration  which,  if  regeneration  of  the  axon  does 
not  occur,  usually  becomes  complete.  If  conditions 
are  favorable  to  regeneration  and  the  axon  grows  out 
to,  and  makes  physiologic  connection  with,  the  muscle, 
the  cell  recovers. 

The  nerve-cells  of  the  posterior  spinal  root  ganglia 
are  originally  bipolar  ;  they  give  off  but  two  processes. 
Later,  these  two  processes  unite  for  a  short  distance, 
rendering  the  cell-body  unipolar.  Each  process  be- 
comes a  medullated  nerve-fiber ;  one,  distributed  to 
peripheral  structures,  functions  as  a  dendrite ;  the  other 
enters  the  spinal  cord  and  is  undoubtedly  an  axon. 
These  cells  suffer  less  from  a  division  of  their  processes 


CONDUCTIVITY.  157 

than  is  tin  rase  with  the  cells  of  the  spinal  cord  which 
uive  oil'  eil'erent  fibers. 

Xcrve-cells  dispatch  impulses  through  their  axons ; 
they  are  excited  by  stimulation  of  their  dend rites.  A 
nerve-fiber,  if  stimulated  midway  in  its  course,  trans- 
mits impulses  in  both  directions,  but  a  visible  result 
occurs  at  one  end  only.  In  the  case  of  an  efferent 
nerve-fiber, — a  motor  fiber,  for  example, — the  only 
appreciable  result  is  muscular  contraction  (except  that, 
by  means  of  a  galvanometer,  an  action  current  may  be 
slmwn  to  travel  along  the  nerve  in  both  directions) ;  no 
change  appears  to  be  caused  in  the  motor  cell  by  the 
entrance  of  the  impulse.  In  the  case  of  an  afferent 
nerve-fiber,  stimulated  midway  between  the  periphery 
and  the  spinal  cord,  the  visible  result  is  brought  about 
by  the  central  discharge  of  the  impulse  in  the  spinal 
cord  ;  no  effect  can  be  shown  to  occur  at  the  periphery. 
When  an  impulse  travels  along  a  nerve-fiber,  it  spreads 
into  any  branches  that  are  given  off;  the  result  of  this 
is  that  if  one  branch  of  a  motor  nerve-fiber  be  stimu- 
lated near  its  muscular  termination,  the  impulse  which 
I >asses  up  the  fiber  toward  the  spinal  cord  will  spread 
into  any  branch  that  happens  to  be  given  off  at  a 
higher  level,  and  traveling  down  this,  may  cause  the 
contraction  of  another  muscle-fiber.  This  is  called  a 
pseudo=reflex.  It  is  probable  that  a  similar  event  may 
occur  on  the  stimulation  of  the  central  termination  of 
an  afferent  nerve-fiber  within  the  spinal  cord  ;  the  im- 
pulse passing  back  along  the  fiber  may  spread  through 
a  collateral  branch  which  is  given  off  from  a  point 
nearer  to  the  parent  cell,  and  stimulate  other  nerve-cells 
in  the  neighborhood  of  which  this  collateral  ends.  (See 
Pig.  7.) 

Nerve-fibers  do  not  seem  to  be  susceptible  of  fatigue ; 
they  may  be  stimulated  for  many  hours  without  loss  of 
irritability  or  conductivity;  their  terminations,  how- 


158  MUSCLE  AND  NERVE. 

ever,  are  readily  fatigued.  The  conductivity  of  a 
nerve-fiber  may  be  temporarily  suppressed  by  freezing, 
or  by  pressure,  or  by  exposure  to  ether  vapor,  etc. ; 
also,  as  we  have  seen,  by  the  passage  of  a  constant 
current.  If  a  nerve  be  crushed,  its  conductivity  at 
this  point  is  destroyed.  If  a  nerve  be  divided  and  the 
two  ends  brought  together,  an  impulse  cannot  be  trans- 
mitted across  the  gap,  continuity  of  the  axis-cylinder 
being  necessary  to  conduction. 

The  Chemical  Composition  of  Muscle. — Muscle 
consists  of  the  following  constituents:  water,  75^  ; 
proteids,  including  paramyosinogen,  myosinogen,  and 
albumin,  20  ^  ;  fats,  glycogen,  phosphoearnic  acid,  and 
inorganic  salts,  in  small  quantities;  and  waste  products 
of  muscular  metabolism,  such  as  kreatin,  xanthin  bases, 
sarcolactic  acid,  etc. 

Mammalian  muscle,  when  its  blood  supply  is  shut 
off,  very  soon  loses  its  irritability,  and  before  long  goes  ! 
into  rigor  mortis.  In  this  condition  it  is  less  elastic  ' 
and  less  extensible,  and,  if  no  resistance  be  offered,  it 
shortens ;  like  that  of  contracting  muscle,  its  reaction 
becomes  slightly  acid.  The  rigidity  depends  upon  the 
precipitation  or  coagulation  of  paramyosinogen  and  myo- 
sinogen, these  being  converted  into  insoluble  myosin. 
If  perfectly  fresh  muscle  be  frozen,  and  subjected  to 
pressure,  there  may  be  expressed  from  it  a  liquid  of 
syrupy  consistence  called  muscle  plasma.  If  kept  cold, 
the  plasma  remains  liquid,  but  if  warmed,  it  clots  ; 
from  the  clot  separates  a  serum,  of  which  the  reaction 
is  acid.  The  clot  consists  of  myosin ;  the  serum  con- 
tains albumin.  The  proteids  of  muscle  may  be  ex- 
tracted by  means  of  a  10%  solution  of  ammonium 
chlorid,  or  a  5  %  solution  of  magnesium  sulphate  ;  on 
dilution,  the  extract  clots,  especially  if  it  be  kept  warm. 
If  before  clotting  occurs  the  extract  be  heated,  the 
different  proteids  will  be  found  to  coagulate  at  different 


QUESTIONS.  159 

temperatures.  Paramyosinogen,  a  globulin,  precipi- 
tates by  heat  at  47°  C.  ;  myosinogen,  a  proteid  with 
many  of  the  characters  of  a  globulin,  at  56°  C1.;  myo- 
globulin,  at  6*3°  C.  ;  albumin,  similar  to  serum  albu- 
min, at  about  73°  C.  The  last  two  occur  in  quite 
-mall  amounts.  If  a  living  muscle  is  heated  gradually, 
its  vitality  is  entirely  lost,  with  its  loss  of  irritability, 
when  it  has  readied  a  temperature  sufficient  to  coagu- 
late the  proteid  of  the  lowest  coagulation  temperature ; 
namely,  the  paramyosinogen  at  47°  C. 

QUESTIONS  FOR  CHAPTER  VIII. 

Is  the  contraction  of  muscle  dependent  on  katabolic  or  anabolic 
changes? 

What  is  meant  by  the  conductivity  of  muscle? 

In  order  to  produce  complete  tetanus,  why  is  the  frequency  of 
Mi  in  illation  that  is  required  less  in  the  case  of  a  fatigued  than  in 
the  case  of  a  fresh  muscle? 

If  an  isolated  muscle  has  been  fatigued  by  continued  stimula- 
tion, why  does  washing  out  its  vessels  with  normal  salt  solution 
tend  toward  the  recovery  of  its  irritability  ? 

Do  the  irritability  and  conductivity  of  a  nerve-fiber  always 
vary  in  the  same  direction  ? 

What  is  the  effect  of  treating  a  muscle  with  the  extract  made 
from  a  fatigued  muscle? 

If  on  passing  a  constant  current  through  a  muscle  the  intensity 
of  the  current  be  suddenly  raised,  at  which  electrode  will  contrac- 
tion begin  ? 

On  stimulating  a  nerve-trunk  in  the  intact  body  with  the  con- 
stant current,  by  the  application  of  which  electrode  may  we  expect 
to  >ncceed  with  the  weakest  current? 

'  If  in  this  respect  the  response  is  abnormal,  what  are  we  to 
conclude? 

If  a  muscle  fails  to  respond  to  the  induced  current,  but  ia 
h.v] u>rirritable  to  the  constant  current,  what  must  we  conclude? 

If  a  nerve  has  been  divided,  how  can  we  determine  when  its 
Regeneration  is  complete? 

What  causes  an  extremity  to  "  go  to  sleep  "  ? 


CHAPTER  IX. 
THE  NERVOUS  SYSTEM. 

The  spinal  cord,  in  the  grouping  of  its  nerve-cells 
and  in  its  relation  to  the  tissues  of  the  different  parts 
of  the  body,  shows  a  segmental  arrangement,  though 
each  segment  is  intimately  connected  with  the  rest  of 
the  central  nervous  system. 

From  each  segment  arises  a  pair  of  spinal  nerves, 
through  which  relations  with  a  particular  segment  of 
the  body  are  established ;  there  is,  however,  an  over- 
lapping of  the  innervation  of  a  particular  body  seg- 
ment, so  that  a  given  muscle  receives  nerve-fibers  from 
two  or  three  segments  of  the  cord ;  this  is  especially 
the  case  with  the  muscles  of  the  limbs.  In  conse- 
quence of  this  arrangement,  a  lesion  which  is  strictly 
confined  to  one  segment  of  the  cord  never  deprives  any 
one  muscle  of  its  nerve  supply. 

Each  spinal  nerve  is  connected  with  the  cord  by  two 
roots,  a  ventral,  or  anterior,  and  a  dorsal,  or  posterior, 
root,  and  each  of  these,  where  it  joins  the  cord,  is  di- 
vided into  several  small  rootlets,  which  are  shown  in 
figure  6.  If  the  anterior  nerve=root  be  divided,  as  at 
a,  degeneration  of  the  peripheral  portion  of  the  root 
occurs,  and  many  nerve-fibers  will  be  found  to  degen- 
erate in  the  common  nerve-trunk  as  far  as  its  termina- 
tions in  the  muscles  and  sympathetic  system.  The 
fibers  of  the  anterior  root  arise  from  cells  which  are 
situated  in  the  gray  matter  of  the  cord,  at  the  level  of 

160 


11 


"isw.  6  and  7. 


162  THE  NERVOUS  SYSTEM. 

each  fiber's  exit.  The  portion  of  the  anterior  root  which 
remains  in  continuity  with  the  cord  does  not  degenerate 
at  once,  for  it  has  not  been  separated  from  its  parent 
cell  as  is  the  case  with  the  portion  peripheral  to  the 
lesion. 

Division  of  the  posterior  spinal  nerve-root  at  a  point 
between  the  root  ganglion  and  the  cord,  as  at  6,  figure 
6,  leads  to  degeneration  of  the  rootlets  which  are  left  in 
connection  with  the  cord,  and  degeneration  of  the  pos- 
terior root-fibers  may  be  traced  within  the  cord,  up- 
ward as  far  as  the  spinal  bulb,  downward  for  a  short 
distance*  only.  No  degeneration  occurs  peripheral  to 
the  lesion,  for  the  posterior  root-fibers  are  the  axons  of 
posterior  root-ganglion  cells,  and  only  that  part  of  a 
fiber  which  is  cut  off  from  its  parent  ganglion  cell  is 
destroyed.  If  the  posterior  root=ganglion  is  removed 
or  crushed,  the  resulting  degeneration  destroys  not  only 
the  nerve-fibers  which  have  grown  from  the  ganglion 
into  the  spinal  cord,  but  those  also  which  are  distrib- 
uted to' the  periphery  through  the  spinal  nerve-trunk. 
Division  of  the  spinal  nerve=trunk  at  a  point  periph- 
eral to  the  root-ganglion  causes  degeneration,  peripheral 
to  the  lesion,  of  all  its  fibers  ;  central  to  the  lesion,  of 
none. 

Figure  7  shows  the  cell  connection  of  the  fibers  of 
both  roots.  It  will  be  noticed  that  the  peripheral  pro- 
cess of  one  posterior  root-ganglion  cell  is  represented 
as  turning  aside  into  the  anterior  nerve-root,  instead  of 
accompanying  its  fellows  down  the  spinal  nerve-trunk. 
The  fibers  which  follow  this  course  are  distributed  to 
the  membranes  of  the  cord,  etc. 

If  the  nerve-roots  be  divided  as  shown  in  figure  8, 
and  the  peripheral  cut  end  of  the  anterior  root  be 
stimulated  at  «,  there  will  result  a  contraction  of  the 
muscle  Mj  to  which  some  of  the  fibers  of  this  nerve  are 


Figs.  8  and  9. 


164  THE  NERVOUS  SYSTEM. 

distributed.  This  result  will  not  be  prevented  by  pre- 
vious destruction  of  the  posterior  root-ganglion,  and 
degeneration  of  the  posterior  root-fibers.  The  anterior 
root  contains  motor  nerve-fibers  which  are  the  axons  of 
spinal  cells.  Stimulation  of  the  central  cut  end  of  the 
anterior  nerve-root,  at  by  produces  no  visible  effect,  for 
the  resulting  nerve  impulses  are  evidently  unable  to 
spread  to  other  neurones  within  the  cord,  though  they 
probably  reach  the  motor  cells  whose  axons  are  stimu- 
lated. 

On  stimulation  of  the  central  cut  end  of  the  posterior 
nerve=root,  at  c,  there  may  occur  a  reflex  contraction 
of  the  muscle  IT,  and,  if  the  spinal  cord  be  intact 
and  connected  with  the  brain,  sensation.  The  nerve 
impulses  excited  in  the  posterior  root-fibers  enter  the 
cord  and  are  transmitted  by  the  ascending  branches  of 
these  fibers  toward  the  brain,  and  by  their  collateral 
branches  (Fig.  7)  to  the  motor  cells  of  the  gray  matter. 
The  motor  cells  are  thus  stimulated,  and  dispatch 
impulses  through  the  anterior  root  to  the  muscles  which 
they  innervate.  Stimulation  of  the  peripheral  cut  end 
of  the  posterior  root,  at  d,  produces,  as  far  as  can  be 
determined,  no  result.  Impulses  will  reach  the  peri- 
pheral terminations  of  the  posterior  root-fibers  in,  for 
instance,  the  skin;  but,  even  if  the  impulse  actually 
reaches  the  structures  in  which  the  fiber  ends,  no  eifect 
seems  to  be  produced. 

The  fibers  of  the  anterior  nerve-roots  are  efferent ; 
they  transmit  impulses  from  the  cord  to  the  periphery. 
The  fibers  of  the  posterior  nerve-roots  are  afferent; 
they  transmit  impulses  from  the  periphery  to  the  spinal 
cord.  An  afferent  neurone  and  an  efferent  neurone 
together  constitute  the  simplest  form  of  reflex  arc.  A 
more  elaborate  form  of  reflex  arc,  including  three 
neurones,  is  shown  in  figure  9.  As  will  be  seen,  this 


THE  SPINAL  CORD.  165 

form  allows  a  more  widespread  reflex,  through  the 
stimulation  of  a  greater  number  of  motor  cells.  The 
axons  of  the  central,  or  mediate,  cells  do  not  leave  the 
central  nervous  system,  but  ascend  and  descend  the 
mrd,  thus  bringing  different  levels  into  communication 
with  one  another.  Some  cross  the  median  line  and 
afford  a  basis  for  crossed  reflexes  ;  neurones  of  this  class 
are  called  com  miss  urn  I. 

The  stimulation  of  the  anterior  root  may  give  rise  to 
sensation  or  to  reflexes,  for,  as  has  been  mentioned 
above,  some  of  the  posterior  root-fibers  bend  back 
toward  the  cord  through  the  anterior  root  (Fig.  7) ; 
this  is  called  recurrent  sensibility. 

In  some  of  the  lower  animals,  for  instance,  the  fish, 
reflexes  may  be  carried  on  by  one  segment  of  the  cord 
after  it  has  been  isolated  from  the  rest.  As  a  general 
rule,  the  reflex  irritability  of  the  spinal  cord  is  in- 
creased by  excluding  the  impulses  which  normally 
descend  from  the  brain.  In  the  spinal  animal — that 
is,  one  whose  cord,  or  the  greater  portion  of  it,  has  been 
separated  from  the  brain — it  is  easier  to  predict  the 
kind  of  reflex  that  will  be  evoked  by  a  given  stimulus. 
If  a  spinal  dog  be  held  in  the  vertical  'position,  the 
stretching  of  the  skin  of  the  pendent  legs  will  give  rise 
to  a  reflex  raising  of  these.  A  minimal  stimulus 
applied  to  the  skin  will  provoke  reflex  contraction  of 
muscles  on  the  same  side  of  the  body  ;  if  the  intensity 
of  the  stimulus  be  raised,  the  reflex  may  spread  to  the 
opposite  side  also.  Reflexes  spread  tailward  more 
readily  than  head  ward  ;  it  is  more  difficult  to  cause 
reflex  movement  of  the  foreleg  by  stimulation  of  the 
skin  of  the  hinder  part  of  the  body  than  to  cause  move- 
ments of  the  hind  limb  by  stimulating  anteriorly.  It 
is  impossible  to  cause  reflex  simultaneous  contraction 
of  antagonistic  muscles ;  if  the  flexors  of  a  limb  con- 


166  THE  NERVOUS  SYSTEM. 

tract,  the  extensors  relax,  and  vice  versa.  The  relaxa- 
tion is  due  to  an  inhibition  of  the  motor  cells  which 
control  the  antagonistic  muscles.  The  skeletal  muscles 
possess  a  tone  which  is  of  reflex  origin  ;  they  are  kept 
in  a  state  of  slight  tonic  contraction  by  weak  motor 
impulses  which  continually  reach  them  from  the  spinal 
centers,  the  activity  of  these  centers  resulting  from  the 
constant  arrival  of  afferent  nerve  impulses  from  the 
periphery.  If  the  motor  cells  be  inhibited  by  impulses 
coming  to  them  from  the  brain,  or  from  a  contracting 
antagonistic  muscle  through  afferent  nerves,  their  ac- 
tivity is  lessened  and  the  muscle  which  they  govern  is 
allowed  to  relax  ;  its  tone  disappears.  The  division  of 
its  nerve  supply  puts  an  end  to  the  tone  of  a  muscle, 
as  may  be  readily  understood.  During  sleep  muscular 
tone  disappears.  When  a  muscle  loses  its  tone,  it  also 
loses  what  is  known  as  myotatic  irritability,  which 
consists  in  the  power  of  a  muscle,  when  stretched,  to 
respond  to  a  mechanical  stimulus.  The  knee=jerk 
which  is  evoked  by  tapping  the  patellar  tendon  when 
the  extensor  muscles  are  put  on  the  stretch  depends 
on  myotatic  irritability ;  it  is  not  a  true  reflex,  but  is  a 
response  to  the  direct  mechanical  stimulation  of  the 
extensors,  by  the  sudden  extra  tension  resulting  from 
the  tap  on  the  tendon.  Although  it  is  not  a  reflex 
contraction,  it  is,  nevertheless,  dependent  on  the  ex- 
istence of  reflex  muscular  tone;  an  injury  to  the  reflex 
arc,  upon  the  integrity  of  which  muscular  tone  depends, 
abolishes  the  knee-jerk ;  this  is  the  case  in  tabes  dor- 
salis,  in  which  the  posterior  nerve-roots  are  affected. 
The  knee-jerk  also  disappears  when  injury  is  done  to 
the  lumbar  region  of  the  cord,  wherein  lie  the  motor 
cells  concerned.  On  the  other  hand,  a  lesion  situated 
above  this  region  may,  by  preventing  cerebral  inhibi- 
tion from  reaching  these  cells,  render  them  more  irri- 


THE  SYMPATHETIC  SYSTEM.  1G7 

table  than  in  the  normal  condition,  and  result  in  exag- 
geration of  the  knee-jerk.  The  extent  or  absence  of 
myotatic  irritability  is,  consequently,  a  symptom  of 
diagnostic  import.  The  condition  of  the  reflexes 
innervated  by  different  portions  of  the  spinal  cord  is  of 
givat  assistance  in  determining  the  position  of  a  lesion; 
as  instances,  the  following  may  be  mentioned:  the 
scapular  reflex,  controlled  by  the  fifth  cervical  to  the 
first  thoracic  segments;  palmar  reflex,  seventh  cervical 
to  first  thoracic;  epigastric  reflex,  fourth  to  seventh 
thoracic ;  abdominal  reflex,  seventh  to  eleventh  thoracic ; 
crenmsteric  reflex,  first  to  third  lumbar ;  knee-jerk, 
second  to  fourth  lumbar;  gluteal  reflex,  fourth  and  fifth 
lumbar ;  plantar  reflex,  first  and  second  sacral ;  Achilles 
tendon  reflex,  third  to  fifth  sacral.  These  centers 
become  hyperirritable  when,  by  injury  to  the  pyramidal 
tracts,  the  control  exercised  by  the  brain  is  eliminated, 
though,  in  man,  complete  division  of  the  cord  is 
followed  by  depression  of  the  centers  situated  below  the 
lesion.  The  reflexes  are  abolished  by  degeneration  of 
the  spinal  centers  which  control  them ;  the  muscles 
concerned  show  the  reaction  of  degeneration,  are  hyper- 
irri table  to  the  constant  current,  lose  their  irritability 
to  the  induced  current,  and  finally  atrophy. 

The  Sympathetic  System. — In  the  thoracic  and 
upper  lumbar  regions  many  of  the  nerve-fibers  of  the 
anterior  and  posterior  spinal  nerve-roots  do  not  pass  out 
to  the  periphery  through  the  corresponding  nerve-trunk, 
1m t  enter  the  sympathetic  system  through  the  white 
rami  communicantes.  The  efferent  fibers  which  follow 
this  course  probably  originate  from  a  group  of  small 
nerve-cells  which  in  these  regions  of  the  cord  are  situ- 
ated in  the  dorsolateral  portion  of  the  anterior  horn,  the 
group  being  known  as  the  intarmedio-lateral.  These 
efferent  fibers  are  medullated,  like  the  other  fibers  of 


168  THE  NERVOUS  SYSTEM. 

the  anterior  root,  but  are  smaller  than  the  rest.  They 
all  end  in  one  or  other  of  the  sympathetic  ganglia,  and 
are  called  pre=ganglionic  sympathetic  fibers.  The 
sympathetic  system  includes  two  chains  of  lateral,  or 
vertebral,  ganglia  ;  and  collateral,  or  prevertebral,  gan- 
glia which  are  found  in  the  solar  plexus,  mesenteric 
plexus,  and,  smaller  ones,  in  close  proximity  to  the 
viscera. 

The  pre-ganglionic  sympathetic  fibers  which  are  con- 
cerned in  the  innervation  of  the  vessels,  glands,  or 
musculature  of  the  abdominal  and  thoracic  viscera, 
pass  through  the  lateral  sympathetic  chain,  to  end  in 
one  of  the  prevertebral  ganglia.  Here  they  make 
physiologic  connection  with  sympathetic  nerve-cells, 
the  relation  being  one  of  contact.  From  the  ganglion 
cells  are  given  off  the  post=ganglionic  fibers,  usually 
nonmedullated,  which  reach  the  tissue  concerned  (Fig.  5). 

The  pre-ganglionic  sympathetic  fibers  which  are  con- 
cerned in  the  innervation  of  the  vessels  of  the  skeletal 
muscles  or  in  the  innervation  of  the  vessels,  plain 
muscle,  and  glands  of  the  skin,  end  in  one  or  other  of 
the  ganglia  of  the  lateral  chain.  The  corresponding 
post-ganglionic  fibers,  which  originate  here,  pass,  by 
way  of  the  gray  rami  communicantes,  into  the  spinal 
nerves  and  thus  reach  the  periphery  (Fig.  4). 

The  posterior  root-fibers  which  enter  the  sympathetic 
system  are  distributed  to  the  viscera  (Fig.  10),  and 
form  one  of  the  channels  through  which  afferent 
impulses  pass  from  the  viscera  to  the  central  nervous 
system.  Afferent  impulses  are  also  carried  from  the 
heart,  lungs,  liver,  stomach,  etc.,  by  the  pneumogastric 
nerve  to  the  medulla,  and  from  the  pelvic  viscera  by 
the  second,  third,  and  fourth  sacral  nerves  to  the  spinal 
cord.  The  pain  resulting  from  disease  of  the  viscera 
is  often  referred  by  the  patient  to  a  definite  area  of  the 


Fig.  10.— The  course  of  an  afferent  sympathetic  fiber. 


170  THE  NERVOUS  SYSTEM. 

skin;  this  area  being  that  which  is  supplied  with 
afferent  fibers  by  the  same  dorsal  spinal  nerve-root 
which  transmits  afferent  impulses  from  the  viscus  in 
question.  Even  in  the  case  of  the  skin,  with  which 
we  are  so  familiar,  it  is  only  through  past  experience 
that  we  are  able  to  localize  the  point  of  origin  of  a 
given  cutaneous  sensation.  It  would  seem  that  the 
afferent  nerve-fibers  which  enter  the  cord  through  a 
given  nerve-root,  whether  they  be  cutaneous  or  visceral, 
make  very  similar  connections  within  the  central 
nervous  system.  Thus  we  are  very  apt  to  be  misled 
into  confusing  the  sensation  resulting  from  an  unusual 
visceral  irritation  with  those  which  arise  from  stimula- 
tion of  an  area  whose  afferent  fibers  may  discharge 
their  impulses  at  much  the  same  point  within  the  cord, 
and  do  so  more  frequently.  Not  only  does  this  con- 
fusion of  sensations  exist;  even  the  reflexes  which 
may  be  excited  by  stimulation  of  a  given  cutaneous 
area  are  intensified  by  irritation  of  the  viscus  whose 
afferent  fibers  enter  through  the  same  nerve-root. 

Whatever  the  destination  of  an  efferent  pre-gangli- 
onic  sympathetic  nerve-fiber,  it  leaves  the  spinal  cord 
in  the  thoracic  or  upper  lumbar  region,  and  originates 
from  a  cell  situated  in  the  cord  at  the  level  where  it 
emerges.  These  pre-ganglionic  fibers  all  end  in  sym- 
pathetic ganglia,  and  the  post-ganglionic  fibers,  which 
originate  from  the  ganglion  cells,  are  all  distributed  to 
cells  (plain  muscle,  of  the  vessels,  viscera,  and  skin, 
cardiac  muscle,  and  gland  cells)  the  activity  of  which 
is  involuntary.  The  sympathetic  system  supplies 
nerve-fibers  of  various  function;  as,  vasoconstrictors 
and  vasodilators,  of  wide  distribution ;  viscero-motor 
fibers,  for  the  spleen,  uterus  and  Fallopian  tubes,  intes- 
tines, etc.;  cardio-augmentors  ;  viscero-inhibitory  fibers, 
such  as  those  supplied  to  the  stomach  and  intestines; 


Till;  SYMPATHETIC  SYSTEM.  171 

pupillo- dilators  ;  secretory  fibers  for  the  salivary,  lacri- 
nial,  and  sweat  glands,  and  for  the  small  glands  of  the 
oral,  nasal,  and  pharyngeal  mucous  membranes;  pilo- 
inotors,  which  control  the  plain  muscle  of  the  skin  and 
bring  about  the  erection  of  the  hair  and  the  condition 
known  as  goose-skin. 

The  arrangement  of  two  other  sets  of  peripheral 
nerve-fibers,  one  set  emerging  from  the  central  nervous 
>vstom  in  certain  cranial  nerves,  the  other,  in  the  (second) 
third  (and  fourth)  sacral  nerves,  resembles  that  of  the 
sympathetic  nerve-fibers.  These  fibers,  also,  are  dis- 
tributed to  gland  cells,  cardiac  and  plain  muscle-fibers. 
Each  set  consists  of  pre-gangl ionic  and  post-gangl  ionic 
fibers.  The  fibers  included  in  the  cranial  set  vary  in 
function.  They  are  :  pupillo-constrictors  and  fibers  of 
visual  accommodation,  in  the  third  cranial  nerve ;  in 
the  seventh  and  ninth  cranial  nerves,  secretory  fibers 
for  the  salivary  glands,  and  glands  of  the  lips  and 
check,  and  vasodilators  for  the  salivary  glands,  tongue, 
soft  palate,  and  floor  of  the  mouth  ;  in  the  tenth  and 
eleventh  cranial  nerves,  viscero-motors  for  the  esopha- 
gus, stomach,  small  intestines,  ascending  and  horizontal 
eol<»n;  broncho-constrictors;  cardio-inhibifory  fibers; 
and  secretory  fibers  for  the  gastric  glands  and  pancreas. 
The  fibers  of  this  class  which  leave  the  cord  in  the 
sacral  nerves  all  pass  through  the  nervus  erigens  ;  they 
an-  viscero-motors  for  the  bladder,  descending  colon, 
and  rectum  ;  vasodilators  for  the  mucous  membrane  of 
the  rectum  and  external  genitalia,  and  inhibitory  fibers 
for  the  plain  muscle  of  the  latter. 

After  division  of  the  extrinsic  nerves  of  the  intes- 
tines, peristalsis  may  be  even  more  vigorous  than  usual, 
and  is  probably  controlled  by  a  local  nervous  mechanism 
which  acts  reflexly.  Stimulation  of  the  mucous  mem- 
brane still  causes  the  characteristic  contraction  above, 


172  THE  NERVOUS  SYSTEM. 

and  inhibition  below,  the  point  stimulated.  Between 
the  muscular  coats  of  the  alimentary  canal,  extending 
from  the  lower  part  of  the  esophagus  to  the  anus,  is 
the  ganglionated  plexus  of  Auerbach,  and  in  the  sub- 
mucosa  is  Meissner's  plexus ;  these  appear  to  act  as  the 
local  reflex  mechanism  for  the  peristalsis  of  the  intes- 
tines. Normally  an  influence  over  peristalsis  is  ex- 
erted through  the  motor  fibers  of  the  pneumogastric 
and  inhibitory  fibers  of  the  sympathetic  nerves. 

Returning  to  the  afferent  nerve-fibers,  which  enter 
the  cord  through  the  posterior  nerve-roots,  we  have  to 
consider  the  channels  through  which  various  sensations 
and  reflexes  are  provoked.  These  fibers  are  distributed 
to  the  skin,  muscles,  tendons,  viscera,  and,  in  fact,  to 
all  parts  of  the  body,  save  those  which  receive  similar 
fibers  through  the  cranial  nerves.  The  skin  is  supplied 
with  fibers  whose  peripheral  terminations  have  been 
specialized  in  such  a  way  that  they  are  irritable  to  a 
particular  form  of  stimulus.  One  set  is  stimulated  by 
the  application  of  heat,  another  by  cold,  and  a  third  by 
pressure.  In  addition,  there  are  fibers  of  wider  cuta- 
neous distribution,  the  endings  of  which  are  less  spe- 
cialized for  response  to  given  forms  of  stimulus ;  the 
sensation  resulting  from  stimulation  of  these  depends 
on  the  intensity  of  the  stimulus ;  weak  stimulation 
gives  rise  to  an  indefinite  sensation  known  as  common 
sensibility;  if  the  stimulus  be  strong,  no  matter  whether 
it  consist  in  the  application  of  pressure,  heat,  cold, 
chemical  irritants,  or  electric  stimulation,  the  resulting 
sensation  is  one  of  pain.  However,  in  order  to  induce 
pain  the  intensity  of  the  stimulus  must  be  greater  than 
is  required  to  cause  a  sensation  of,  for  instance,  pressure, 
when  it  is  applied  to  a  specific  nerve-ending.  The 
degree  of  temperature  to  which  the  ending  of  a  cold- 
nerve  responds  depends  upon  the  temperature  of  the 


AFFERENT  NERVE-FIBERS.  173 

>kiu  at  the  time  of  application,  and  upon  the  rapidity 
with  which  the  lowering  of  the  temperature  is  brought 
about.  The  endings  of  cold-nerves  may  also  be  stimu- 
lated by  the  application  of  heat,  but  the  resulting  sen- 
sation is  one  of  cold.  The  endings  of  cold-nerves  are 
more  numerous  than  those  of  heat-nerves  ;  the  endings 
of  pain-nerves,  more  numerous  than  those  of  either  of 
the  other  varieties. 

Many  of  the  afferent  nerve-fibers  which  are  distrib- 
uted to  the  skeletal  muscles  end  in  muscle  spindles, 
which  consist  of  several  muscle-fibers  inclosed  in  a 
connective-tissue  covering,  within  which  the  nerve- 
til  MTS  ramify  upon  the  muscle.  When  a  muscle  con- 
tracts or  is  stretched,  these  nerve-endings  are  stimulated, 
impulses  are  transmitted  to  the  central  nervous  system 
and  give  rise  to  sensations  which  are  described  as 
muscle  sense.  By  means  of  these  impressions,  we  form 
an  idea  of  the  force  and  extent  of  the  contraction  of 
our  muscles,  and  of  the  resistance  opposed  to  their  con- 
traction ;  the  pressure  nerves  of  the  skin  are  also  im- 
portant in  this  respect. 

The  afferent  nerves  of  the  viscera  are  concerned,  for 

,f 

tin-  most  part,  in  reflexes  of  which  we  are  unconscious; 
it  is  seldom  that  we  experience  visceral  sensations ; 
operations  upon  the  normal  abdominal  viscera  are  pain- 
less ;  yet  under  certain  circumstances  these  nerves  may 
transmit  impulses  which  excite  intense  pain. 

As  was  stated  al»ve,the  central  axons  of  the  posterior 
spinal  root-ganglion  cells,  on  entering  the  cord,  divide 
into  ascending  and  descending  branches.  The  former 
are  the  longer,  but  vary  in  length.  Both  branches 
finally  end  in  the  gray  matter,  some  ascending  as  far  as 
the  medulla  ;  both  give  off  collaterals  (Fig.  7),  which 
also  end  in  the  gray  matter.  The  course  of  these  fibers 
is  in  the  posterior,  or  dorsal,  columns  of  white  matter, 


174  THE  NERVOUS  SYSTEM. 

each  of  which  is  subdivided  into  a  dorsomedian  and  a 
dorsolateral  tract  (Figs.  11,  12).  The  fibers  ascend  at 
first  in  the  dorsolateral  tract,  but,  in  the  case  of  those  of 
the  lumbar  nerves  which  reach  the  medulla,  they  later- 
pass  over  into  the  dorsomedian  tract,  and  thus  reach  the 
dorsomedian  nucleus,  or  nucleus  gracilis  of  the  medulla, 
where  they  end.  The  dorsolateral  tract,  when  it  reaches 
the  medulla,  consists  chiefly  of  fibers  which  carry 
impulses  from  the  upper  extremities ;  these  fibers  end 
in  the  dorsolateral  nucleus,  or  nucleus  cuneatus. 
These  two  nuclei  serve  as  cell  stations  for  the  forward- 
ing of  impulses  to  the  cerebellum  and  to  the  cerebrum, 
in  response  to  impulses  received  from  the  periphery. 
They  contain  nerve-cells  whose  axons  follow  several 
different  paths ;  some,  the  internal  arcuate  fibers,  curve 
ventral  ward,  cross  the  median  line,  and  ascend  in  the  fillet, 
or  lemniscus,  on  the  opposite  side,  toward  the  cerebrum 
(Fig.  11).  Probably,  only  the  minority  of  these  reach 
the  cortex ;  many  of  them  end  at  lower  levels  in,  for 
instance,  the  optic  thalamus  and  corpora  quadrigemina. 
The  optic  thalamus  seems  to  afford  another  cell  station 
on  the  way  to  the  cerebral  cortex.  In  the  internal  cap- 
sule the  ascending  fibers  are  found  in  the  posterior 
portion  of  the  dorsal  limb. 

The  dorsal  nuclei  are  connected  with  the  cerebellum, 
through  the  restiform  body,  by  two  sets  of  fibers ;  one 
set,  arising  from  the  cells  of  these  nuclei,  passes  directly 
into  the  restiform  body  on  the  same  side ;  another  set,  the 
external  arcuate  fibers,  follows  the  same  course  as  the 
internal  arcuates  until,  the  median  line  having  been 
crossed,  they  reach  the  surface,  and,  passing  in  front  of 
the  pyramid,  enter  the  restiform  body,  and  so,  the  cere- 
bellum. The  fibers  which  thus  reach  the  cerebellum 
carry  impulses  to  the  roof  nuclei  and  cortex  of  the 
inferior  vermis.  It  is  highly  probable  that  impulses 


Fig.  11. 


176 


THE  NERVOUS  SYSTEM. 


which  are  concerned  in  muscle=sense  ascend  the  cord 
and  reach  the  cerebellum  and  cerebrum  over  the  paths 
just  described;  there  is  some  evidence  that  the  im- 
pulses concerned  in  tactile  sensibility,  pressure  sense, 
also  follow  this  course. 

If  the  posterior  nerve-roots  be  divided,  the  degen- 
eration of  fibers  within  the  cord  is  confined  to  those  in 
the  dorsal  columns.  Division  of  the  cord  itself  is  fol- 
lowed by  the  degeneration  of  not  only  the  dorsal  column 


ln/v\A~ 


Fig.  12. — The  ascending  and  descending  tracts  of  the  spinal  cord,  in  cross-section. 

fibers  which  have  entered  below  the  point  of  lesion, 
but  of  fibers  situated  in  other  tracts.  Figure  9  shows 
central  cells  whose  axons  ascend  and  descend  the  cord 
for  short  distances,  in  that  part  of  the  white  matter 
which  is  adjacent  to  the  gray.  Many  of  these  will  be 
divided  in  making  a  transverse  section  of  the  cord,  and 
degeneration  will  occur  in  that  portion  of  the  fiber 
which  is  separated  from  its  parent  cell ;  in  those  which 
have  grown  from  below  upward,  and  are  divided,  de- 


Fig.  13. — Serial  sections  showing  the  course  and  connections  of  the  direct  cere- 
bellar  tract.     (The  upper  .section  is  disproportionately  reduced.) 

12 


178  THE  NERVOUS  SYSTEM. 

generation  will  occur  above  the  lesion ;  those  which 
have  grown  downward,  and  are  divided,  will  degenerate 
below  the  lesion.  In  addition  to  these,  fibers  of  much 
greater  length  will  be  found  to  degenerate  both  above 
and  below  the  point  of  section. 

One  distinctly  marked  ascending  tract,  or  tract  of 
fibers  which  degenerate  above  the  point  of  section,  is 
the  direct  cerebellar  tract  (Figs.  12  and  13).  The 
fibers  which  constitute  this  tract  originate  from  a  group 
of  cells  which  persists  throughout  the  thoracic  cord,  and 
is  known  as  the  column  of  Clarke,  or  the  vesicular  cyl- 
inder. The  group  lies  at  the  base  of  the  posterior  horn 
of  gray  matter,  and  toward  its  median  border.  In  the 
neighborhood  of  these  cells  many  of  the  dorsal  column 
collaterals  end,  and  thus  bring  the  group  under  the 
influence  of  the  afferent  impulses  which  enter  through 
the  posterior  roots.  The  direct  cerebellar  tract  ascends 
the  cord  without  undergoing  decussation  and  enters  the 
cerebellum  through  the  restiform  body,  its  fibers  ending 
chiefly  in  the  cortex  of  the  vermis,  partly  on  the  same, 
partly  on  the  opposite  side.  What  afferent  impulses 
are  carried  by  this  tract  is  uncertain.  It  must  be  re- 
membered that  impulses  which  reach  the  cerebellum 
may  cause  the  dispatch  of  cerebellar  impulses  to  the 
cerebrum,  for  the  two  are  intimately  connected  through 
the  superior  cerebellar  peduncle,  or  brachium  conjunc- 
tivum  (Fig.  13). 

Another  ascending  tract  is  that  of  Gowers,  or  the 
anterolateral  ascending  tract  (Figs.  12, 14).  Its  fibers 
originate  from  cells  situated  in  the  gray  matter,  on  the 
same  and  on  the  opposite  side  of  the  cord ;  they  pass 
for  the  most  part  into  the  cerebellum,  some  ascending 
as  far  as  the  level  of  the  inferior  corpus  quadrigeminum, 
and  then  curving  downward  into  the  vermis ;  others 
entering  the  cerebellum  through  the  restiform  body. 


WucV. 


"ig.  14. — Serial  sections  showing  the  course  and  connections  of  the  anterolateral 
ascending  tract.    (Upper  section  disproportionately  reduced.) 


180  THE  NERVOUS  SYSTEM. 

Mixed  with  these  fibers  are  some  which  do  not  enter 
the  cerebellum,  but  end  in  the  corpora  quadrigeminj 
and  optic  thalamus.  This  tract  appears  to  convey  im- 
pulses concerned  in  temperature  sensations  and  pain. 
Destruction  of  the  ventrolateral  portion  of  the  spinal 
cord  on  one  side  leads  to  loss  of  the  perception  of  pain- 
ful stimuli,  of  heat  and  cold,  when  these  are  applied  to 
the  skin  on  the  opposite  side  of  the  body  below  the 
lesion. 

Of  the  cranial  nerves,  the  first,  second,  fifth,  both 
divisions  of  the  eighth,  the  ninth,  and  tenth  contain 
afferent  nerve-fibers.  In  the  case  of  the  fifth,  eighth, 
ninth,  and  tenth,  these  afferent  fibers  behave  much  as 
do  the  afferent  fibers  which  enter  the  cord  ;  on  entering 
the  medulla  they  divide  into  ascending  and  descending 
branches,  the  latter  being,  however,  the  longer ;  from 
these,  collateral  branches  are  given  off. 

The  afferent  fibers  of  the  tenth  cranial  nerve,  vagus 
or  pneumogastric,  have  a  wide  distribution  and  carry 
impulses  from  the  heart,  lungs,  pharynx,  larynx,  trachea, 
esophagus,  stomach,  intestines,  liver,  pancreas,  and 
spleen.  These  fibers,  on  entering  the  medulla,  divide 
into  short  ascending  branches  which  end  in  the  nucleus 
alae  cinereae,  and  long  descending  branches  which  form 
the  tractus  solitarius,  or  solitary  bundle.  These  give 
off  many  collaterals  which  end  amongst  cells,  that  are 
scattered  along  this  tract  and  form  the  nucleus  of  the 
solitary  bundle.  The  axons  of  the  cells  of  these  two 
nuclei  follow  a  course  similar  to  that  of  the  internal 
arcuate  fibers  which  originate  from  the  cells  of  the  gracile 
and  cuneate  nuclei.  They  curve  through  the  retictilar 
formation  to  the  median  line,  cross  it,  and  ascend  in  the 
opposite  fillet ;  some  fibers,  however,  enter  the  posterior 
longitudinal  bundle,  and  ascend  in  this  toward  the 
brain  (Fig.  15).  The  further  course  of  the  fibers  which 


Fie.  15.— The  afferent  fibers  of  tbe  niiiih  and  tenth  cruuiul  nerves. 


182  THE  NERVOUS  SYSTEM. 

enter  the  fillet  is  the  same  as  that  already  described 
(Fig.  11).  These  fibers,  before  they  decussate,  give 
off  collaterals  which  end  in  the  reticular  formation,  and 
may  be  supposed  to  influence  the  cells  of  the  cardio- 
inhibitory,  respiratory,  and  vasoconstrictor  centers  which 
are  situated  in  this  neighborhood. 

The  ninth  cranial  nerve,  or  glossopharyngeal,  con- 
tains afferent  fibers  which  carry  impulses  from  the 
tongue,  pharynx,  Eustachian  tube,  etc.  Its  central  con- 
nections are  much  the  same  as  those  of  the  pneumogas- 
tric  (Fig.  15). 

The  cochlear,  or  auditory  division  of  the  eighth 
cranial  nerve,  consists  of  afferent  fibers  which  are  dis- 
tributed to  the  cochlea,  and  carry  auditory  impulses. 
These  fibers  are  the  axons  of  the  bipolar  cells  of  the 
spiral  ganglion;  in  the  medulla  they  end  in  two  nuclei, 
the  ventral  and  dorsal  cochlear  nuclei.  The  axons  from 
the  cells  which  form  these  nuclei  pass  through  the  tra- 
pezium and  striae  acusticse,  as  shown  in  figure  16,  to  the 
superior  olive  on  the  opposite  side ;  some,  however,  end 
in  the  superior  olive  on  the  same  side.  Many  of  the 
fibers  end  in  the  olive  ;  others  pass  through  it  and  ascend, 
with  the  axons  of  olivary  cells,  in  the  lateral  fillet. 
The  fibers  of  the  lateral  fillet  end  on  the  same  side  in 
the  inferior  corpus  quadrigeminum,  in  the  medial  gen- 
iculate  body,  and  a  few  in  the  superior  corpus  quad- 
rigeminum ;  and  on  the  opposite  side,  in  the  inferior 
corpus  quadrigeminum.  From  the  geniculate  body  im- 
pulses are  forwarded  to  the  cerebrum  ;  the  corpora  quad- 
rigemina  probably  act  as  centers  through  which  sounds 
may  bring  about  reflex  movements  of  the  head  and  eyes. 
The  auditory  impulses  pass  chiefly  to  the  opposite  side 
of  the  brain,  but  it  will  be  seen  from  the  diagram  (Fig. 
16)  that  there  are  several  means  of  communication  with 
the  same  side  of  the  brain. 


Fig.  16. — The  cochlear  nerve. 


184  THE  NERVOUS  SYSTEM. 

The  vestibular  division  of  the  eighth  cranial  nerve 

consists  of  afferent  fibers  which  arise  from  the  vesti- 
bular ganglion  cells.  The  peripheral  processes  of  these 
bipolar  cells  end  in  the  vestibule  and  semicircular 
canals.  This  nerve  carries  afferent  impulses,  by  means 
of  which  we  are  informed  of  movements  of  the  head 
or  of  the  body  as  a  whole,  and  which  assist  in  the 
reflex  and  voluntary  maintenance  of  equilibrium.  On 
entering  the  medulla  at  the  lower  border  of  the  pons, 
they  end,  for  the  most  part,  in  four  nuclei — namely,  the 
superior,  lateral,  and  medial  vestibular  nuclei,  and  the 
nucleus  of  the  descending,  or  spinal,  vestibular  root. 
Some  fibers  pass  directly  into  the  cerebellum.  The 
axons  of  the  vestibular  nuclear  cells  follow  several 
different  routes ;  axons  from  each  nucleus  enter,  and 
ascend  in  the  median  fillet  and  posterior  longitudinal 
bundle,  mainly  on  the  opposite  side ;  from  the  lateral 
and  superior  nuclei  fibers  also  pass  into  the  cerebellum, 
while  others  descend  the  cord  ;  both  these  sets  probably 
play  a  part  in  reflex  equilibration  (Fig.  17). 

The  fifth  cranial  nerve,  trigeminus  or  trifacial,  con- 
tains afferent  fibers  which  carry  impulses  from  the  skin 
of  the  face,  from  the  conjunctiva,  and  from  the  mucous 
membranes  of  the  nose  and  mouth.  Some  of  the  fibers 
distributed  to  the  tongue  may  cany  impulses  which 
result  in  sensations  of  taste.  The  afferent  fibers  of  the 
trigeminus  originate  from  cells  situated  in  the  Gasserian 
ganglion.  On  entering  the  pons  they  divide  into  very 
short  ascending  branches  which  end  in  the  chief  trige= 
minal  nucleus,  and  very  long  descending  branches,  the 
spinal  root,  whose  collaterals  end  amongst  the  cells  of 
the  substantia  gelatinosa  which  forms  the  nucleus  of  the 
spinal  root.  The  axons  which  arise  in  these  nuclei  give 
off  collaterals  in  the  reticular  formation,  and  probably 


AFFERENT  NERVE-FIBERS.  185 

ascend  in  the  median  fillet  on  the  opposite  side  of  the 
median  line  (Fig.  18). 

The  second  cranial,  or  optic,  nerve  differs  entirely 
in  its  method  of  development  from  the  other  afferent 
nerves  that  we  have  considered ;  it  may,  however,  be 
described  with  them.  It  consists  chiefly  of  afferent 
fibers  which  are  the  axons  of  retinal  ganglion  cells. 
Light  which  falls  upon  the  retina  does  not  stimulate 
these  cells  directly,  but  takes  effect  upon  the  rods  and 
coin's  of  the  outer  layer.  Between  the  rod  and  cone 
cells  and  the  ganglion  cells,  mediate  the  bipolar  neurones 
of  the  retina.  The  axons  of  the  retinal  ganglion  cells 
enter  the  optic  nerve,  and  pass  along  it  to  the  optic 
chiasma ;  here  the  fibers  from  the  nasal  half  of  the 
retina,  and  some  of  those  which  originate  from  the  cells 
in  the  macula  lutea,  decussate,  and  enter  the  opposite 
optic  tract;  the  fibers  from  the  temporal  half  of  the 
retina  do  not  cross,  but  proceed  through  the  optic  tract 
on  the  same  side  toward  the  brain.  The  optic  tract, 
then,  contains  fibers  from  the  temporal  half  of  the 
homonymous  retina,  fibers  from  the  maculae  luteae  of  both 
eyes,  and  fibers  from  the  nasal  half  of  the  contralateral 
ret  inn.  These  fibers  reach  and  end  in  the  external  geni- 
culate  body,  the  pulvinar,  and  the  anterior  corpus  quad- 
rigeminum.  Axons  originating  from  the  cells  of  these 
bodies  transmit  impulses  through  the  optic  radiation  to 
the  occipital  cortex,  which  constitutes  the  visual  area 
of  the  brain.  The  anterior  corpus  quadrigeminum  forms 
a  center  through  which  visual  reflexes  are  probably 
inaugurated  ;  fibers  originate  here  which  decussate  and 
descend  through  the  posterior  longitudinal  bundle  into 
the  spinal  cord,  giving  off,  on  their  way,  collaterals 
which  terminate  in  the  motor  nuclei  of  the  nerves  which 
innervate  the  muscles  of  the  eye.  They  very  probably 


Fig.  17.— The  vestibular  nerve. 


Fig.  18.— The  afferent  fibers  of  the  fifth  cranial  nerve. 


188  THE  NERVOUS  SYSTEM. 

also  bring  about  reflex  turning  of  the  head  in  response 
to  visual  stimuli  (Fig.  19). 

The  first  cranial,  or  olfactory,  nerve  consists  of  the 
axons  of  cells  situated  in  the  olfactory  mucous  mem- 
brane of  the  nose ;  the  dendrites  of  these  cells  reach 
the  surface ;  their  axons  pass  through  the  cribriform 
plate  of  the  ethmoid  bone,  and  enter  the  olfactory  bulb. 
The  axons  end  here,  in  the  olfactory  glomerali,  in  con- 
tact with  the  dendrites  of  the  mitral  cells,  whose  axons 
form  the  second  link  in  the  chain  which  transmits 
olfactory  impulses  toward  the  brain.  The  mitral  cell 
axons  run  in  two  directions  ;  one  set  enters  the  anterior 
commissure,  and,  passing  through  it,  reaches,  on  the 
one  hand,  the  opposite  olfactory  bulb,  on  the  other,  the 
opposite  hippocampus.  Of  the  other  set,  the  majority 
of  fibers  pass  through  the  lateral  olfactory  gyrus  to  the 
uncus,  where  they  end.  The  fibers  of  the  medial  root 
end  in  the  trigonum,  where  they  make  cell  connections 
which  bring  them  into  communication  with  other  parts 
of  the  olfactory  area.  From  the  cells  of  the  uncus,  in 
contact  with  which  the  fibers  of  the  lateral  root  end, 
axons  pass  to  the  hippocampus.  The  hippocampal 
neurones,  in  turn,  make,  through  the  fornix,  manifold 
connections,  some  of  which  are  shown  in  figure  20. 
Some  of  the  fibers  end  in  the  nucleus  habenulse,  whence 
neurones  descend  through  Meynert's  retroflexed  bundle ; 
others  end  in  the  corpus  mammillare,  and  make  con- 
nections with  neurones  whose  axons  divide  into  two 
branches,  one  ascending  to  the  anterior  nucleus  of  the 
optic  thalamus,  the  other  descending. 

Sensory  Cortical  Areas. — Certain  areas  of  the  cor- 
tex cerebri  are  closely  associated  with  sensation,  and  it  is 
to  these  areas  that  impulses  provocative  of  sensation  are 
carried.  Destruction  of  the  left  occipital  lobe  leads  to 
blindness  of  the  left  half  of  each  retina ;  destruction  of 


Fig.  19.— The  optic  nerve. 


190  THE  NERVOUS  SYSTEM. 

the  right  occipital  lobe  causes  blindness  of  the  right 
half  of  each  retina.  The  cortical  area  lying  on  either 
side  of  the  calcarine  fissure  is  probably  concerned  in  re- 
ception of  impulses  from  the  macula  lutea,  or  area  of 
most  distinct  vision,  of  each  eye.  Figure  21  shows 
the  visual  and  other  sensory  areas  of  the  cortex,  those 
for  cutaneous  sensibility  being,  however,  of  doubtful 
location. 

Descending  Tracts  of  the  Spinal  Cord. — Hav- 
ing considered  the  channels  through  which  afferent 
nerve  impulses  are  carried  from  the  periphery  to  the 
brain,  there  remain  for  description  the  connections 
between  higher  centers  and  the  peripheral  efferent 
neurones.  After  transverse  sections  of  the  spinal  cord, 
degeneration  of  certain  nerve-fibers  occurs  below  the 
lesion  ;  these  degenerated  fibers  are,  of  course,  the  pro- 
cesses of  cells  which  are  situated  at  various  levels 
above  the  lesion.  There  are  many  cells  in  the  gray 
matter  of  the  cord  whose  axons  enter  the  white  columns, 
and  ascend  or  descend,  for  comparatively  short  dis- 
tances, to  end  in  the  gray  matter  at  different  levels ;  on 
their  way  through  the  white  matter  they  give  off  col- 
laterals which  also  enter  and  end  in  the  gray  matter 
(Fig.  9).  In  addition  to  these,  there  are  fibers  which 
descend  into  the  cord  from  higher  levels.  Two  such 
tracts  have  already  been  mentioned — namely,  the  fibers 
which  descend  from  the  vestibular  nuclei  (Fig.  17), 
and  those  which  descend  in  the  posterior  longitudinal 
bundle  from  the  superior  corpus  quadrigeminum  (Fig. 
19).  Both  these  sets  of  fibers  descend  through  the 
ventrolateral  columns  of  the  cord,  and  give  off  collat- 
erals to  the  gray  matter.  Fibers  also  descend,  in  all 
probability,  from  the  cerebellum,  though  these  may  be 
interrupted  by  cell  stations  in  the  inferior  olives,  or  in 
the  pons.  There  is  no  doubt  that  the  cerebellum, 


Fig.  20. — Olfactory  connections. 


192  THE  NERVOUS  SYSTEM. 

either  directly  or  indirectly,  exerts  an  influence  over 
the  motor  neurones  of  the  cord,  for  its  removal  results 
in  marked  interference  with  the  coordination  of  move- 
ments and  the  maintenance  of  equilibrium.  Another 
set  of  fibers  descends  from  the  red  nucleus  into  the 
opposite  half  of  the  spinal  cord,  and  is  found  just 
medial  to  the  direct  cerebellar  tract.  Two  descending 
tracts,  with  the  course  and  function  of  which  we  are 
better  acquainted,  are  the  direct  and  crossed  pyramidal 
tracts.  It  is  perhaps  better  to  call  them  the  ventral 
and  lateral  pyramidal  tracts  (Fig.  12).  They  originate 
chiefly  from  cells  which  are  situated  in  what  are  known 
as  the  motor  areas  of  the  cortex. 

It  has  been  found  that  the  stimulation  of  certain 
areas  of  the  cortex  cerebri  results  in  the  contraction  of 
certain  groups  of  muscles.  Figure  22  shows  the  dis- 
tribution of  these  areas. 

In  these  areas  are  large  pyramidal  cells, — so  called 
on  account  of  their  shape, — whose  axons  pass  through 
the  corona  radiata  to  the  internal  capsule,  of  which 
they  form  the  knee  and  anterior  two-thirds  of  the  pos- 
terior limb  (Fig.  23).  The  arrangement  of  the  pyra- 
midal fibers  in  the  internal  capsule  shows  a  certain 
correspondence  to  that  of  the  motor  areas  from  which 
they  originate ;  most  anteriorly  are  situated  the  fibers 
from  the  motor  area  for  the  eyes,  then  come  those  for 
the  head,  and  these  are  followed  in  order  by  those  for 
the  tongue  and  mouth,  shoulder,  elbow,  wrist,  fingers, 
trunk,  hip,  knee,  toes.  The  arrangement  of  these 
fibers  in  definite  groups  according  to  their  origin  per- 
sists throughout  their  course,  though  even  in  the  internal 
capsule  there  is  some  admixture.  The  pyramidal  fibers 
pass  down  through  the  middle  portion  of  the  crusta  of 
the  cerebral  peduncle,  and  through  the  ventral  portion 
of  the  pons,  into  the  medulla,  where  they  form  the 


DESCENDING  TRACTS  OF  THE  SPINAL  CORD.      193 

pyramid  from  which  their  name  is  derived.  At  the 
ln\\cr  cud  of  the  medulla  the  majority  of  the  fibers 
cross,  in  the  pyramidal  decussation,  into  the  lateral 
pyramidal  tract  on  the  opposite  side,  and,  descending 
the  cord,  end  at  successive  levels  in  the  gray  matter 
near  Clarke's  column.  The  stimulation  of  the  motor 
cells  of  the 'anterior  horn  must  therefore  entail  the 
mediation  of  an  intervening  neurone,  which  perhaps 
stimulates  several  motor  cells.  Not  all  the  pyramidal 
fibers  decussate  in  the  medulla;  a  few  pass  into  the 
lateral  pyramidal  tract  of  the  same  side,  some  descend 
in  the  homonymous  ventral  pyramidal  tract.  The 
fibers  of  the  ventral  pyramidal  tract  decussate  at  various 
levels  of  the  cord  and  end  in  the  gray  matter  of  the 
opposite  half.  The  fibers  which,  without  crossing,  de- 
scend the  lateral  pyramidal  tract  end  in  the  gray  matter 
on  the  same  side  of  the  cord.  By  far  the  majority  of 
the  pyramidal  fibers,  then,  cross  in  the  medulla;  of  the 
remainder,  the  majority  cross  before  they  end  ;  only  a 
ie\v  end  without  crossing  the  median  line.  Each  half 
of  the  brain  controls  muscles  on  the  opposite  side  of  the 
body.  As  the  pyramidal  tracts  descend  the  cord  they 
gradually  diminish  in  bulk,  for  fibers  leatfe  them  at 
each  succeeding  level  to  end  in  the  gray  matter.  The 
ventral  pyramidal  tract  disappears  before  reaching  the 
lumbar  region. 

It  is  important  to  note  that  movement  is  not  the 
only  result  of  stimulating  a  given  cortical  area.  If 
carefully  localized  stimulation  be  applied  to  the  motor 
area  for  one  set  of  muscles,  the  antagonists  of  this  set 
relax  ;  for  example,  stimulation  of  an  area  of  flexion 
causes  contraction  of  the  flexor  muscles  concerned  and 
simultaneous  relaxation  of  the  extensors  which  are  an- 
tagonistic to  them.  The  cortex  can  therefore  both  pro- 
voke and  inhibit  muscular  contraction.  Evidence  of 
13 


Fig.  21. — Sensory  areas  of  the  cortex  cerebri. 


Fig.  22. — Motor  areas  of  the  cortex  cerebrL 


196  THE  NERVOUS  SYSTEM. 

the  removal  of  this  cortical  inhibition  is  seen  on  division 
of  the  pyramids  :  the  spinal  centers,  released  from  con- 
trol, respond  more  readily  than  usual  to  the  afferent 
impulses  which  reach  them  from  the  periphery,  and 
reflex  muscular  tone  is  exaggerated. 

Some  of  the  motor  fibers  of  the  internal  capsule, 
which,  on  reaching  the  cerebral  peduncle,  lie  medial  to 
the  fibers  of  the  pyramidal  tract,  end  in  the  motor 
nuclei  of  the  cranial  nerves ;  as  is  shown  in  figures 
24  and  25.  In  addition,  it  appears  that  fibers  descend 
through  the  median  fillet,  to  end  in  the  nuclei  of  the 
seventh  and  twelfth  nerves. 

Motor  Cranial  Nerves. — The  third  cranial  nerve, 
oculomotor,  arises  from  a  nucleus  which  consists  of 
several  cell-groups  situated  in  the  floor  of  the  Sylvian 
aqueduct,  at  the  level  of  the  superior  corpora  quadri- 
gemina.  The  most  anteriorly  situated  cells  of  this 
nucleus  appear  to  be  concerned  in  accommodation ; 
the  next,  in  constriction  of  the  pupil ;  those  innervat- 
ing the  muscles  of  the  eyeball — namely,  the  inferior, 
superior,  and  internal  recti,  and  the  inferior  oblique 
muscles — and  the  levator  palpebrse  being  situated 
more  posteriorly.  Some  axons  of  the  third  nerve 
decussate  before  their  exit,  but  the  majority  do  not 
(Fig.  24). 

The  fourth  cranial  nerve,  or  trochlear  nerve,  arises 
from  a  group  of  nerve-cells  which  occupy  much  the 
same  position  as  the  nucleus  of  the  third  nerve,  but  are 
situated  rather  more  posteriorly.  The  axons  of  these 
cells  descend  for  a  short  distance  before  entering  the 
velum,  in  which  they  cross  to  the  opposite  side,  and 
emerge  as  the  fourth  nerve.  This  nerve  innervates  the 
superior  oblique  muscle  of  the  eyeball  (Fig.  24). 

The  smaller  root  of  the  fifth  cranial  nerve  arises 
from  two  nuclei,  the  chief  of  which  is  situated  in  the 


Fig.  23.— Origin  and  course  of  the  ventral  and  lateral  pyramidal  tracts. 


198  THE  NERVOUS  SYSTEM. 

dorsal  portion  of  the  pons ;  the  other  nucleus,  that  of 
the  descending  root,  consists  of  a  group  of  cells  which 
are  scattered  over  a  narrow  area,  from  the  chief  nucleus, 
forward,  to  the  level  of  the  corpora  quadrigemina.  The 
axons  of  these  cells  join  the  lower  branch  of  the  tri- 
geminus,  and  innervate  the  muscles  of  mastication. 
Cortical  fibers,  chiefly  from  the  opposite  hemisphere, 
probably  reach  the  motor  nucleus  of  the  fifth  nerve 
(Fig.  24). 

The  fibers  of  the  sixth  cranial  nerve,  or  abducens, 
arise  from  a  nucleus  which  is  situated  in  the  dorso- 
medial  portion  of  the  pons  in  the  floor  of  the  fourth 
ventricle.  This  nerve  innervates  the  external  rectus 
muscle  of  the  eyeball.  Cortical  fibers  reach  this  nucleus, 
chiefly  from  the  opposite  hemisphere  (Fig.  24).  This 
nucleus  is  brought  under  the  influence  of  the  superior 
corpus  quadrigeminum  through  the  posterior  longi- 
tudinal bundle  (Fig.  19).  The  same  is  true  of  the 
nucleus  of  the  third  nerve. 

The  seventh  cranial,  or  facial  nerve,  arises  from  a 
nucleus  situated  ventrolaterally  from  that  of  the  sixth 
nerve,  and  extending  further  posteriorly.  The  axons 
pass  dorsomedially,  and  run  for  a  short  distance  an- 
teriorly beneath  the  floor  of  the  fourth  ventricle ;  they 
arch  over  the  nucleus  of  the  sixth  nerve,  and  emerge 
ventrally  from  the  lower  border  of  the  pons.  This 
nerve  is  distributed  to  the  muscles  of  the  face.  Corti- 
cal fibers,  chiefly  from  the  opposite  side,  reach  this 
nucleus ;  descending  fibers  of  the  median  fillet  also 
probably  reach  it  (Fig.  24). 

The  motor  fibers  of  the  ninth  cranial,  or  glosso- 
pharyngeal  nerve,  originate  from  the  nucleus  ambiguus, 
which  lies  in  the  reticular  formation  dorsal  to  the  in- 
ferior olive.  Its  axons  proceed  dorsomedially,  turn, 
and  emerge  in  company  with  the  afferent  fibers  of  the 


Fig.  24.— The  efferent  fibers  of  the  third,  fourth,  fifth,  sixth,  and  seventh  cra- 
nial nerves. 


200  THE  NERVOUS  SYSTEM. 

nerve.  The  motor  fibers  of  this  nerve  are  distributed 
to  the  middle  constrictor  muscle  of  the  pharynx,  and  to 
the  stylopharyngeus.  This  nucleus  probably  receives 
cortical  fibers,  mainly  from  the  opposite  side  (Fig.  25). 

The  motor  fibers  of  the  tenth  cranial  nerve,  vagus, 
or  pneumogastric,  also  arise  from  the  nucleus  ambiguus, 
and  its  central  connections  are  the  same  (Fig.  25).  Its 
motor  fibers  are  distributed  to  pharynx  and  esophagus, 
larynx,  bronchial  muscles,  stomach,  and  intestines.  It 
also  contains  cardio-inhibitory  fibers,  and  secretory 
fibers  for  the  gastric  glands  and  pancreas. 

It  is  doubtful  whether  the  cranial  portion  of  the 
eleventh  nerve,  which  also  originates  from  the  nucleus 
ambiguus,  belongs  in  reality  to  this  nerve  or  to  the 
vagus,  which  it  joins.  The  spinal  portion  originates 
from  cells  situated  in  the  lateral  horn  of  the  cervical 
region,  from  the  level  of  the  first  to  the  fifth  or  sixth 
cervical  nerve.  The  spinal  portion  innervates  the 
sternocleidomastoid  and  trapezius  muscles.  The  nuclei 
of  this  nerve  receive  fibers  from  the  opposite  half  of 
the  brain,  and  possibly  a  few  from  the  same  side  (Fig. 
25). 

The  twelfth  cranial,  or  hypoglossal  nerve,  is  the 
motor  nerve  for  the  tongue,  and  arises  from  a  nucleus 
which  lies  close  to  the  median  line  in  the  dorsal  part  of 
the  medulla ;  the  upper  end  of  this  group  of  nerve-cells 
is  just  beneath  the  floor  of  the  fourth  ventricle ;  lower 
down,  it  is  ventral  to  the  central  canal.  It  receives 
fibers  from  the  cortex  cerebri,  chiefly  from  the  opposite 
side,  and  some  descending  fibers  from  the  median  fillet 
(Fig.  25). 


Fig.  25.— The  efferent  fibers  of  the  ninth,  tenth,  eleventh,  and  twelfth  cranial 

nerves. 


202  THE  NERVOUS  SYSTEM. 


THE  CEREBRUM* 

The  cerebral  hemispheres  are  concerned  in  sensation, 
consciousness,  memory,  intelligence,  and  volition.  The 
destruction  of  a  sensory  area  leads  to  loss  of  the  sen- 
sation with  which  the  area  had  to  do ;  for  instance,  re- 
moval of  the  two  occipital  lobes  results  in  complete 
blindness,  though  the  eyes  are  uninjured.  The  pupils, 
however,  continue  to  contract  when  light  falls  on  either 
retina ;  the  reflex  arc  concerned  includes  the  rod  and 
cone  cells  and  the  bipolar  cells  of  the  retina,  the  retinal 
ganglion  cells  and  their  axons,  neurones  of  the  anterior 
corpus  quadrigeminum,  and  those  of  the  third  nerve 
which  innervate  the  constrictor  pupillse.  An  injury  to 
either  of  the  links  in  this  chain  will,  of  course,  put  an 
end  to  the  light-reflex. 

Destruction  of  a  motor  area  results  in  paralysis  of  the 
muscles  which  were  innervated  by  this  portion  of  the 
cortex.  There  may,  in  time,  be  some  recovery  of  move- 
ment, especially  in  young  patients,  but  the  finer  move- 
ments, such  as  those  of  the  hand,  are  permanently  lost. 
The  paralyzed  muscles  may  be  caused  to  contract  re- 
flexly.  Destruction  of  a  sensory  area — e.  </.,  the  visual 
cortex — causes  no  motor  paralysis  ;  in  the  normal  con- 
dition, however,  stimulation  of  the  visual  area  causes 
movements  of  the  eyes.  The  visual  area  is,  neverthe- 
less, not  classed  as  a  motor  area,  for  it  is  evident  that 
the  influence  exerted  over  the  peripheral  motor  neurone 
is  not  a  direct  one. 

The  result  of  a  complete  removal  of  the  cerebral 
hemispheres,  which  in  some  of  the  lower  animals  is 
possible,  varies.  The  frog,  deprived  of  its  hemispheres, 
can,  by  its  appearance,  hardly  be  distinguished  from  a 
normal  frog.  It  is  capable  of  maintaining  its  equi- 
librium, of  leaping  and  swimming,  but  shows  not  the 


THE  CEREBRUM.  203 

slightest  sign  of  memory  or  volition,  and,  save  in  re- 
sponse to  some  stimulus,  never  moves. 

Pigeons  bear  the  operation  well,  and  their  subsequent 
condition  is  similar  to  that  of  the  frog.  Undisturbed, 
they  sleep  most  of  the  time;  but  if  wakened,  may  walk 
jil)out,  clean  their  feathers,  and  if  thrown  into  the  air, 
fly.  They  must,  however,  be  fed,  for,  lacking  volition, 
they  would  otherwise  starve  to  death.  In  time  both  the 
frog  and  the  pigeon  may  begin  to  exhibit  complicated 
reflexes  that  give  the  impression  of  intelligence. 

In  dogs  the  cortex  can  be  completely  removed  only 
by  successive  operations.  If  this  be  accomplished  and 
the  animal  be  kept  alive,  it  shows  entire  loss  of  intelli- 
gence and  of  memory,  but  is  able  to  walk,  and  exhibits 
signs  of  sensation  .and  emotion  ;  the  latter  phenomena 
do  not  prove  that  the  dog  is  conscious;  they  may  be 
the  expression  of  complicated  reflex  response  to  stimuli 
which  are  unperceived  by  the  animal. 

In  man  the  extensive  destruction  of  the  cerebral 
cortex  by  accident  or  disease  is  usually  followed  by 
death  ;  but  small  areas  are  often  rendered  functionless 
in  this  way,  with  the  production  of  characteristic  symp- 
toms. The  destruction  of  the  motor  areas  on  one  side, 
as  has  been  stated,  results  in  paralysis  of  the  corre- 
sponding muscles  on  the  opposite  side  of  the  body; 
this  may  be  accompanied  by  no  loss  of  sensation.  De- 
struction of  the  internal  capsule,  on  the  other  hand,  if 
it  be  complete,  causes  both  motor  and  sensory  paralysis 
of  1 1m  opposite  half  of  the  body.  The  well-being  of  the 
motor  neurones  concerned  in  voluntary  movements  is  not 
all  that  is  necessary  to  the  proper  use  of  our  muscles. 
Movements  in  which  but  one  muscle  is  brought  into 
play  are  exceptional ;  as  a  rule,  we  use  a  group,  or  sev- 
eral groups,  of  muscles  at  one  time,  and  the  successful 
accomplishment  of  the  movement  is  only  possible  if  the 


204  THE  NERVOUS  SYSTEM. 

contraction  of  the  different  members  of  the  group  be  co- 
ordinated by  the  nervous  system.  Coordination  is 
largely  dependent  on  the  reception  of  afferent  im- 
pulses from  the  muscles  themselves,  and  is  conse- 
quently rendered  imperfect  by  a  break  in  the  afferent 
pathway.  Such  is  the  case  in  tabes,  in  which  the  dorsal 
columns  of  the  spinal  cord  are  affected,  and,  conse- 
quently, muscle-sense  is  defective.  In  the  lower  ani- 
mals the  division  of  all  the  dorsal  nerve-roots  which  in- 
nervate a  limb,  leads  to  complete  disuse  of  this  member 
(apesthesia),  though  the  motor  pathway  is  in  no  way  in- 
jured by  the  operation,  and  the  muscles  can  be  caused 
to  contract  by  artificial  stimulation  of  the  motor  corti- 
cal area. 

If  figures  21  and  22  be  examined  together,  it  will  be 
seen  that  by  no  means  the  whole  of  the  cortex  has  been 
mapped  out  into  motor  and  sensory  areas  ;  large  cortical 
fields  intervene,  the  stimulation  of  which  leads  to  no 
visible  result.  These  have  been  called  by  Flechsig 
association  areas,  and  are  perhaps  concerned  with  the 
interpretation  of  sensations,  in  memory,  and  with  intellec- 
tual processes  in  general.  There  are  several  areas  in  the 
cortex  of  the  left  hemisphere  which  are  intimately  con- 
nected with  the  understanding  and  use  of  language.  A 
lesion  strictly  confined  to  the  left  auditory  area,  though 
it  causes  deafness  on  the  right  side,  may  not  interfere 
with  the  understanding  of  spoken  language  or  with 
speech ;  but  if  the  lesion  is  more  wide-spread  and  in- 
cludes the  neighboring  cortical  area,  the  patient  no 
longer  understands  the  words  which  he  can  hear  perfectly 
well  with  the  left  ear.  The  result  seems  to  be  due  to 
an  injury  to  an  association  area,  rather  than  to  the  aud- 
itory area  itself.  The  condition  is  one  of  sensory  apha= 
sia.  Disease  of  part  of  the  left  occipital  lobe  leads  to 
sensory  aphasia  of  a  different  form,  or  alexia ;  in  this, 


THE  CEREBELLUM.  205 

the  defect  consists  in  the  failure  to  understand  written 
language ;  speech  and  the  understanding  of  spoken  lan- 
guage being  retained.  The  posterior  part  of  the  left  infe- 
rior frontal  gyrus,  IJroca's  area,  is  known  as  the  speech 
center.  Disease  of  this  part  of  the  cortex  results  in 
loss  of  speech,  while  spoken  and  written  language  are 
still  understood  ;  this  is  known  as  motor  aphasia.  The 
condition  is  not  due  to  a  paralysis  of  the  muscles  of 
phonation,  though  the  area  corresponds  in  part  to  the 
motor  area  for  the  tongue,  larynx,  etc.  The  patient  can 
still  use  these  muscles,  and  may,  under  the  influence  of 
emotion,  speak  in  a  rational  manner;  sometimes  the 
power  of  singing  is  retained.  It  is  possible,  more 
especially  in  young  patients,  to  regain  the  power  of 
speech,  through  the  education  of  the  corresponding  cen- 
ter on  the  right  side.  The  right  speech  center  may  per- 
haps be  used  to  a  certain  extent  by  the  normal  individ- 
ual, and  this  may  account  for  the  retention  of  emotional 
speech  by  the  aphasic.  Left-handed  individuals,  whose 
peculiarity  perhaps  depends  on  anatomic  superiority,  in 
their  case,  of  the  right  hemisphere  over  the  left,  use  the 
right  speech  center. 

Not  only  are  neighboring  convolutions  connected  with 
one  another  by  means  of  association  fibers,  but  the 
different  lobes  of  each  hemisphere  are  connected  in  the 
same  way  ;  in  addition,  the  two  hemispheres  are  united 
by  association  fibers,  through,  for  example,  the  corpus 
callosum.  Stimulation  of  the  corpus  callosum  can 
through  indirect  excitation  of  the  cortical  motor  areas, 
bilateral  movements. 

The  Cerebellum. — The  voluntary  control  of  move- 
ments, and  more  especially  of  those  concerned  in  progres- 
sion  and  in  the  maintenance  of  equilibrium,  is  very  much 
interfered  with  by  injury  to  the  cerebellum.  As  we  have 
seen,  afferent  impulses  reach  the  cerebellum  through  the 


206  THE  NERVOUS  SYSTEM. 

dorsal,  direct  cerebellar,  and  ascending  anterolateral 
tracts  of  the  spinal  cord,  and  through  the  vestibular 
nerves  from  the  semicircular  canals  ;  it  also  receives  fibers 
from  the  inferior  olives.  It  is,  then,  an  important  station 
for  the  reception  of  afferent  impulses  from  a  wide  periph- 
eral area.  Nevertheless  its  destruction  does  not  result  in 
loss  of  sensation ;  the  impulses  which  reach  the  cerebel- 
lum seem  rather  to  be  concerned  in  unconscious  reflex 
coordination  of  muscular  movement.  The  patient  who 
suffers  from  cerebellar  disease,  and,  consequently,  from 
incoordination  of  movement,  is  perfectly  aware,  even 
when  his  eyes  are  closed,  that  his  motions  are  ill  directed, 
but  lacks  the  power  to  order  them  rightly.  With  con- 
tinued practice  the  defect  may,  to  a  certain  extent,  be 
overcome ;  but  it  would  be  quite  impossible  for  such  an 
individual  to  run  downstairs ;  careful  attention  must  be 
directed  to  each  movement  if  it  is  to  be  carried  out  cor- 
rectly. Although  the  cerebellum  is  connected  with  the 
motor  cells  of  the  spinal  cord  by  descending  fibers,  its 
influence  on  coordination  seems  rather  to  be  exerted 
through  fibers  which  ascend  toward  the  cerebrum,  and 
end  either  in  the  thalamus  or  in  the  cortex.  The  vermis 
is  the  portion  of  the  cerebellum  which  is  concerned  in 
maintaining  equilibrium;  the  function  of  the  large 
lateral  lobes  is  unknown.  The  fibers  which  pass  from 
the  cerebellum  to  the  cerebrum  cross  the  median  line  in 
the  superior  peduncles,  and  end  on  the  opposite  side  in 
the  red  nucleus  or  optic  thalamus ;  from  these  bodies 
impulses  are  carried  to  the  cortex  by  another  set  of 
neurones.  Impulses  pass  in  the  opposite  direction,  from 
the  cerebrum  to  the  cerebellum,  over  fibers  which  con- 
nect the  frontal  and  temporal  cortex  with  the  gray  mat- 
ter of  the  pons,  and  the  gray  matter  of  the  pons  with 
the  opposite  half  of  the  cerebellum.  The  lateral  ves- 
tibular nucleus,  or  Deiters'  nucleus,  probably  acts  as 


THE  SEMICIRCULAR  CANALS.  207 

a  relay  station  for  the  forwarding  of  impulses  from  the 
cerebellum  to  the  gray  matter  of  the  spinal  cord  on  the 
same  side  of  the  median  line.  The  motor  symptoms 
which  follow  injury  to  one  half  of  the  cerebellum  appear 
on  the  side  of  the  lesion ;  this  is  to  be  expected,  since 
the  fibers  which  leave  the  cerebellum  transmit  impulses, 
on  the  one  hand,  to  the  same  side  of  the  cord,  on  the 
other,  to  the  opposite  cerebral  hemisphere ;  and,  as  we 
know,  the  cerebral  control  of  a  muscle  is  exercised  by 
the  opposite  half  of  the  brain. 

The  Semicircular  Canals. — The  afferent  impulses 
which  pass  from  the  semicircular  canals  to  the  central 
nervous  system  are  of  the  utmost  importance  in  the 
conscious  appreciation  of  the  movements  of  the  body 
as  a  whole,  and  of-  its  position,  and  in  the  reflex  and 
voluntary  maintenance  of  equilibrium.  The  nerve- 
h'bers  which  enter  the  medulla  through  the  vestibular 
nerve  are  the  central  axons  of  the  bipolar  vestibu- 
lar ganglion  cells ;  the  peripheral  axons  (or  den- 
drites?)  of  these  cells  are  distributed  to  the  macula 
acustica  of  the  utricle,  and  to  the  cristse  ampullares  of 
the  semicircular  canals.  In  these  structures  the  fibers 
branch,  their  terminal  fibrillse  surrounding  the  bodies 
of  the  hair-cells.  The  hair-cells  are  so  called  on  ac- 
count of  the  hair-like  processes  which  project  from 
their  free  surface  into  the  endolymph  which  fills  the 
membranous  labyrinth.  The  semicircular  canals  on  each 
side  are  arranged  in  the  three  planes  of  space,  at  right 
angles  with  one  another;  consequently,  the  head  cannot 
be  moved  without  causing,  in  one  or  other  of  the  canals, 
a  change  in  the  pressure  which  is  exerted  by  the  endo- 
lymph on  the  hair  processes  of  the  epithelium.  Further, 
the  relations  existing  between  the  arrangement  of  the 
canals  on  the  two  sides  of  the  head  is  such  that  a  change 
of  pressure  on  the  hair  processes  in  one  ampulla  is  accom- 


208  THE  NERVOUS  SYSTEM. 

panied  by  a  change  of  pressure  in  the  opposite  direction 
in  the  ampulla  of  the  parallel  canal  on  the  opposite 
side.  Changes  of  pressure  on  the  hair-cells  cause 
stimulation  of  the  terminations  of  the  vestibular  nerve- 
fibers,  and  these  transmit  impulses  to  the  medulla. 
The  central  connections  of  these  fibers  have  been  dis- 
cussed. Disease  of  or  injury  to  any  of  the  semicir- 
cular canals  may  cause  vertigo;  but  if  all  the  canals 
on  one  side  are  removed,  there  will  be  marked  loss  of 
equilibrium  and  muscular  coordination,  resulting  in  a 
falling  to  the  affected  side  ;  a  result  which  is  especially 
noticeable  in  birds,  which  show  a  very  perfect  develop- 
ment of  the  sense  of  equilibration. 


QUESTIONS  FOR  CHAPTER  IX. 

Compare  the  path  followed  by  a  motor-nerve  impulse  passing  to 
a  skeletal  muscle  with  that  of  an  impulse  which  reaches  involun- 
tary muscle  ? 

How  may  we  determine  whether  the  ventral  nerve-roots  contain 
nerve-fibers  which  have  descended  the  cord  from  a  higher  level  ? 

How  may  we  ascertain  whether  paralysis  of  a  muscle  depends 
upon  injury  to  pyramidal  fibers  or  to  ventral  root-fibers  ? 

In  what  different  ways  may  a  nerve-center  be  directly  influ- 
enced ? 

Injury  to  what  different  structures  causes  a  loss  of  reflex  con- 
traction of  muscle? 

On  stimulation  of  a  motor  cortical  area,  how  many  neurones  are 
concerned  in  the  transmission  of  the  motor  impulse  to  a  muscle- 
fiber? 

Having  divided  a  nerve-trunk,  what  must  be  done  to  prevent 
permanent  paralysis  of  the  muscles  innervated  by  this  nerve  ? 

How  can  you  tell  when  a  divided  nerve  has  renewed  its  connec- 
tion with  a  muscle  ? 

Would  you  expect  the  paralysis  which  results  from  destruction 
of  the  gray  matter  of  the  cord  to  be  permanent  or  otherwise  ? 

To  what  extent  is  the  voluntary  use  of  muscles  affected  by  divi- 
sion of  the  posterior  nerve-roots  ? 


QUESTIONS.  209 

How  can  we  decide,  by  the  examination  of  a  section  of  the  upper 
cervical  conl.  whether  degeiierat i<m  found  in  the  dorsal  column 
was  the  result  of  a  lesion  situated  in  the  lower  cervical  or  lower 
thoracic  region  ? 

Given  three  animals,  A,  B,  and  C  :  the  left  internal  capsule  of 
A  having  been  destroyed,  the  left  half  of  the  spinal  cord  of  B 
having  been  transversely  divided  in  the  thoracic  region,  and  in  C 
all  the  lumbar  and  sacral  posterior  nerve-roots  having  been  divided, 
explain  the  effect  in  each  case,  if  any  exist,  on  the  voluntary 
movements  of  the  left  leg,  and  on  the  left  knee-jerk? 

How  can  we  ascertain,  from  the  nature  and  distribution  of  sen* 
sory  paralysis,  whether  the  causative  lesion  is  situated  in  the  in- 
ternal capsule,  or  consists  in  hemisection  of  the  cord  ? 

What  lesion  will  bring  about  loss  of  voluntary  movement  of  the 
leg,  and  exaggeration  of  the  knee-jerk  ? 

What  lesion  will  cause  incoordination  of  voluntary  movement 
and  loss  of  the  knee-jerk  ? 

How  can  we  determine  the  level  of  a  lesion  of  the  cord  which 
has  brought  about  paralysis  of  the  leg? 

Will  a  lesion  of  the  cord  which  causes  paralysis  of  the  legs 
necessarily  result  in  paralysis  of  their  arterioles? 

How  do  the  results  of  injury  to  the  ventral  nerve-roots  differ, 
with  regard  to  muscular  contraction,  from  those  arising  from  injury 
to  the  dorsal  nerve-roots  ? 

Where  do  peripheral  sensory  nerve-fibers  originate? 

In  respect  to  voluntary  contraction,  reflex  contraction,  and 
sensation,  how  do  the  effects  of  the  following  lesions  differ : 
Destruction  of  the  motor  cortical  area  on  one  side;  destruc- 
tion of  the  internal  capsule  on  one  side  ;  division  of  the  pyramid 
of  the  medulla  ;  and  hemisection  of  the  cord  in  the  lower  cervical 
region  ? 

What  comment  have  you  to  make  on  a  case  in  which  loss  of 
speech  accompanied  paralysis  on  the  left  side  of  the  body? 

How  may  an  animal  be  blinded  without  destroying  visual 
reflexes? 

What  lesions  will  lead  to  a  loss  of  the  pupil  light-reflex  without 
causing  blindness  ? 

What  is  the  result  of  injury  to  or  removal  of  the  semicircular 
eanals? 

14 


CHAPTER  X. 
THE  SPECIAL  SENSES. 

VISION. 
WHEN  light  passes  from  one  medium  into  another  the 

O  A 

density  of  which  differs  from  that  of  the  first,  the  course 
of  those  rays  which  do  not  fall  perpendicularly  upon 
the  surface  of  the  second  medium  is  changed — the  rays 
are  refracted.  As  light  enters  the  eye,  it  passes  from 
the  air  into  the  cornea,  then  into  the  aqueous  humor,  then 
into  the  lens,  and,  traversing  the  vitreous  humor,  reaches 
the  retina.  It  thus  passes  through  four  refracting  sur- 
faces on  its  way  to  the  retina — namely,  the  anterior  and 
posterior  surfaces  of  the  cornea,  which  are  parallel  to  one 
another ;  and  the  anterior  and  posterior  surfaces  of  the 
lens,  which  are  parallel  neither  to  the  corneal  surfaces 
nor  to  each  other.  The  centers  of  curvature  of  all 
these  surfaces  are,  however,  situated  approximately  upon 
one  axis,  so  that  a  ray  of  light  traveling  along  this  axis 
will  suffer  no  refraction  on  its  way  to  the  retina. 
Other  rays  which  enter  the  eye  will  be  refracted  at  each 
of  the  four  surfaces  which  they  traverse.  The  extent 
of  refraction  depends  upon  the  course  of  the  ray,  the 
curvature  of  the  surface,  and  the  difference  in  the  den- 
sity of  the  two  media  separated  by  the  surface.  The 
more  obliquely  a  ray  of  light  cuts  the  refracting  sur- 
face, the  greater  the  curvature  of  the  surface,  and  the 
wider  the  difference  between  the  density  of  the  media, 
the  greater  will  be  the  degree  of  refraction.  Consider- 

210 


VISION.  211 

able  refraction  occurs  at  the  anterior  surface  of  the  cor- 
nea, where  the  light  passes  from  the  air,  the  refractive 
index  <>f  which  is  1.0,  into  the  cornea,  the  refractive 
index  of  which  is  1.37,  its  radius  of  curvature  being 
7.8  mm.  Very  little  refraction  occurs  at  the  posterior 
-urf'ace  of  the  cornea,  since  the  refractive  index  of  the 
aqueous  humor  (1.33)  differs  but  little  from  that  of  the 
cornea.  The  refractive  index  of  the  lens  is  1.43,  the 
radius  of  curvature  of  its  anterior  surface  being,  when 
the  eiliary  muscle  is  at  rest,  10  mm.;  here,  again,  the 
refraction  is  considerable.  The  rays  a  re  again  refracted 
at  the  posterior  surface  of  the  lens,  the  radius  of  curv- 
ature of  this  surface  being  6  mm.;  here  the  rays  pass 
into  the  vitreous  humor,  the  refractive  index  of  which 
is  the  same  as  that  of  the  aqueous  humor  (1.33). 

Tliis  complex  system  of  media  and  refracting  sur- 
faces may,  however,  be  represented  by  what  is  known 
as  the  reduced  eye,  which  consists  of  one  medium  with 
an  index  of  refraction  about  the  same  as  that  of  the 
aqueous  and  vitreous  humors,  bounded  by  one  surface 
with  a  radius  of  curvature  of  5.1  mm.  The  refraction 
Buffered  by  a  ray  of  light  on  entering  such  an  eye, 
would  be  equal  to  the  total  refraction  suffered,  on  its 
way  to  the  retina,  by  a  ray  forming  the  same  angle  with 
the  principal  axis  of  the  normal  eye.  This  imaginary 
refracting  surface  lies  between  the  cornea  and  the  lens. 
Tin-  nodal  point  of  the 'reduced  eye — that  is,  the  center 
of  curvature  of  its  refracting  surface — is  situated  0.47 
nun.  in  front  of  the  posterior  surface  of  the  lens,  and, 
of  course,  on  the  principal  axis.  Such  a  reduced  eye 
represents  the  normal  eye  only  when  the  ciliary  muscle 
is  at  rest.  The  refracting  surface  of  a  reduced  eye  that 
shall  accurately  represent  the  refraction  that  occurs  in 
the  normal  eye  when  the  ciliary  muscle  is  contracted 
must  have  a  greater  curvature.  Rays  of  light  the 


212  THE  SPECIAL  SENSES. 

course  of  which  is  parallel  to  the  principal  axis  are  re- 
fracted to  meet,  at  the  posterior  principal  focus,  on  the 
principal  axis ;  when  the  ciliary  muscle  is  at  rest,  the 
posterior  principal  focus  falls  upon  the  retina.  The  an- 
terior principal  focus  lies  12.9  mm.  in  front  of  the  cor- 
nea, on  the  principal  axis ;  rays  which  emanate  from 
this  point  are,  within  the  eye,  rendered  parallel  to  the 
principal  axis.  The  cardinal  points  of  the  system  are 
the  anterior  and  posterior  principal  foci,  the  nodal  point, 
and  the  principal  point,  the  latter  being  the  point  where 
the  optic  axis  cuts  the  refracting  surface  of  the  reduced 
eye,  and  being  situated  in  the  aqueous  humor  2.2  mm. 
behind  the  anterior  surface  of  the  cornea. 

Rays  of  light  which  fall  perpendicularly  upon  the 
refracting  surface  of  the  reduced  eye  suffer  no  refrac- 
tion, but  pass  on  through  the  nodal  point  to  the  retina. 
Consequently,  a  ray  of  light  emanating  from  a  point 
above  the  principal  axis,  and  falling  perpendicular  to 
the  refracting  surface,  will  reach  the  retina  at  a  point 
below  the  principal  axis ;  a  ray  coming  from  a  point 
situated  below  the  principal  axis  will  strike  the  retina 
above  it.  Light  stimulates  certain  structures  in  the 
retina,  and,  as  a  result,  nerve  impulses  are  transmitted 
to  the  brain,  there  giving  rise  to  sensations.  By 
experience  we  learn  to  associate  sensations  resulting 
from  stimulation  of  the  lower  part  of  the  retina  with 
light  emanating  from  a  point  situated  above  the  optic 
axis;  sensations  resulting  from  stimulation  of  the  upper 
part  of  the  retina,  with  light  coming  from  a  source 
situated  below  the  optic  axis;  the  same  is  true  of 
stimulation  of  the  lateral  portions  of  the  retina — the 
resulting  sensations  are  associated  with  points  on  the 
opposite  side  of  the  axis. 

The  formation  of  an  image  on  the  retina  is  shown  in 
figure  26.  With  the  exception  of  the  principal  ray, 


VISION.  213 

winch  falls  perpendicularly  upon  the  refracting  surface 
of  the  reduced  eye  (this  surface  is  represented  in  the 
figure  by  a  broken  line),  the  diverging  rays  which  are 
reflected  from  a  given  point  of  the  surface  of  an  opaque 
object,  and  which  enter  the  eye,  are  refracted  to  meet 
the  principal  ray  upon  the  retina,  and  form  here  an 
image  of  the  point  from  which  they  were  reflected.  In 
like  manner,  there  are  formed  images  of  other  equidis- 
tant points  of  the  object  at  the  points  where  their  prin- 
cipal rays  strike  the  retina.  In  this  way  an  image  of 


Fig.  26. — Formation  of  an  image  on  the  retipa. 

the   whole    object   may    be    formed;    it  is,  of  course, 
inverted. 

When  the  ciliary  muscle  of  the  eye  is  at  rest,  rays 
of  light  which  diverge  from  a  point  near  the  eye  are 
not,  by  the  time  they  reach  the  retina,  brought  to  a 
focus ;  consequently,  they  form,  instead  of  a  sharp 
image,  a  diffusion  circle.  In  order  that  a  sharp  image 
of  a  near  object  may  be  formed  on  the  retina,  the  focal 
distance  of  the  eye  must  be  shortened.  This  is  known 
as  accommodation,  and  is  accomplished  by  the  contrac- 


214  THE  SPECIAL  SENSES. 

tion  of  the  ciliary  muscle.  When  this  muscle  is  at 
rest,  the  lens  is  flattened  by  the  tension  to  which  the 
suspensory  ligament  and  capsule  are  subjected  owing  to 
intraocular  pressure.  When  the  ciliary  muscle  con- 
tracts, it  stretches  the  elastic  choroid  coat,  and  pulls 
forward  its  anterior  margin,  to  which  is  attached  the 
suspensory  ligament.  The  suspensory  ligament  and 
capsule  being  thus  slackened,  and  the  pressure  on  the 
inclosed  lens  being  reduced,  the  anterior  surface  of  the 
elastic  lens  bulges  forward,  its  curvature  is  increased, 
and,  with  the  curvature,  the  power  of  refraction.  The 
image  of  an  object  which  is  near  the  eye  may  thus  be 
formed  upon  the  retina.  The  normal  eye  cannot,  how- 
ever, be  accommodated  for  objects  which  lie  within  10 
or  12  centimeters  of  the  cornea.  This  is  known  as  the 
near-point  of  distinct  vision.  Since  parallel  rays  are 
brought  to  a  focus  upon  the  retina  of  the  resting  eye, 
the  far-point  of  vision  is  at  an  infinite  distance. 

Accommodation  is  accompanied  by  constriction  of 
the  pupil,  and  by  convergence  of  the  optic  axes  of  the 
two  eyes  ;  to  a  certain  extent  the  latter  may,  by  prac- 
tice, be  dissociated  from  the  two  former.  The  motor 
impulses  concerned  in  causing  these  events  reach  the 
eye  through  the  third  nerve ;  pre-ganglionic  fibers 
which  carry  motor  impulses  to  the  ciliary  muscle  and 
constrictor  pupillse  end  in  the  ciliary  ganglion,  and 
make  connection  here  with  cells  whose  post-ganglionic 
fibers  are  distributed  to  these  structures.  Although  the 
ciliary  muscle  is  of  the  unstriped  variety,  it  is  under 
the  control  of  the  will,  and  the  eye  may,  by  practice, 
be  accommodated  for  short  distances  without  fixing  the 
attention  upon  near  objects.  No  direct  voluntary  con- 
trol can  be  exercised  over  the  size  of  the  pupil,  but  it 
may  be  indirectly  varied  through  voluntary  contraction 
or  relaxation  of  the  ciliary  muscle,  with  which  its 


MYOPIA.  215 

movements  are  associated.  Light,  when  it  falls  on 
cither  retina,  onuses  n-tiex  constriction  of  both  pupils; 
the  afferent  impulses  concerned  being  probably  carried 
to  the  anterior  corpus  quadrigeminum,  whence  impulses 
are  dispatched  to  the  nuclei  of  the  third  cranial  nerves. 
The  size  of  the  pupil  is  also  influenced  by  pupillo-dila- 
tor  fibers,  which  leave  the  spinal  cord  in  the  second 
thoracic  nerve  and  enter  the  sympathetic  chain  to  end 
in  the  superior  cervical  sympathetic  ganglion.  Con- 
nection is  here  made  with  nerve-cells  whose  axons  form 
post-ganglionic  fibers  that  pass  through  the  cavernous 
plexus  to  the  Gasserian  ganglion,  and  thence  with  the 
ophthalmic  division  of  the  fifth  nerve  to  the  eye,  reach- 
ing the  latter  through  the  long  ciliary  nerves.  The 
pupillo-dilator  center  is  probably  situated  in  close  prox- 
imity to  the  nucleus  of  the  third  nerve,  and  appears  to 
exert  a  tonic  influence,  for  division  of  the  cervical 
sympathetic  is  followed  by  constriction  of  the  pupil. 
Dilatation  of  the  pupil  accompanies  relaxation  of  the 
ciliary  muscle;  it  may  be  caused  reflexly  by  stimula- 
tion of  afferent  nerves,  as,  for  instance,  by  tickling  the 
palm  of  the  hand,  or  by  applying  a  painful  stimulus  to 
the  back  of  the  neck ;  it  is  influenced  by  the  emotions. 
It  is  probable  that  dilatation  depends  upon  contraction 
of  radially  disposed  cells  of  the  iris,  but  whether  or  no 
these  cells  are  plain  muscle-cells,  is  uncertain.  Both 
accommodation  and  the  size  of  the  pupil  are  affected 
by  certain  drugs ;  atropin,  for  example,  paralyzes  the 
terminations  of  the  motor  nerve-fibers  of  the  ciliary 
and  constrictor  muscles,  and  probably  stimulates  the 
fibers  which  cause  dilatation ;  physostigmin,  on  the 
other  hand,  stimulates  the  terminations  of  these  nerves, 
and  paralyzes  the  dilators. 

Myopia,  or  short  sight,  depends  upon  the  fact  that 
the  posterior  principal  focus  falls  in  front  of,  instead  of 


216  THE  SPECIAL  SENSES. 

upon,  the  retina.  In  the  hypermetropic,  or  long-sighted 
eye,  the  posterior  principal  focus  lies  behind  the  retina. 
The  former  condition  usually  results  from  the  antero- 
posterior  diameter  of  the  eye  being  abnormally  great ; 
the  most  frequent  cause  of  hypermetropia  is  an  abnor- 
mally small  anteroposterior  diameter  of  the  eyeball. 
The  hypermetropic  eye  has,  when  the  ciliary  muscle  is 
at  rest,  neither  near-  nor  far-point  of  distinct  vision, 
for  rays  which  come  from  even  an  infinite  distance  are 
not  brought  to  a  focus  by  the  time  they  reach  the  retina, 
and  still  more  is  this  the  case  with  those  emanating 
from  objects  which  are  near  the  eye  ;  the  condition  may, 
however,  be  compensated  to  a  certain  extent  by  accom- 
modation, but  the  near-point  of  vision  is  always  further 
from  the  eye  than  the  normal.  The  near-point  of  dis- 
tinct vision  of  the  myopic  eye  is  nearer  to  the  eye  than 
that  of  the  emmetropic  or  normal  eye,  consequently  a 
larger  image  of  a  small  object  may  be  formed  on  the 
retina  of  a  myopic  eye,  and  small  objects  may  thus  be 
seen  more  distinctly  by  a  short-sighted  individual  than 
by  one  whose  vision  is  normal.  The  far-point  of  dis- 
tinct vision  of  the  myopic  eye  is  at  a  comparatively 
short  distance,  for  only  the  divergent  rays  which  fall 
upon  the  cornea  can  be  focused  upon  the  retina ;  paral- 
lel rays  are  brought  to  a  focus  before  reaching  it.  As 
age  advances,  the  power  of  accommodation  is  impaired, 
through  weakness  of  the  ciliary  muscle  and  lessening 
of  the  elasticity  of  the  lens,  the  condition  being  known 
as  presbyopia;  the  near-point  of  distinct  vision  grad- 
ually recedes  from  the  eye,  but  there  is  no  interference 
with  the  vision  of  distant  objects. 

Astigmatism  is  an  irregularity  of  vision  which  is 
usually  dependent  on  differences  in  the  curvature  of  the 
cornea.  In  the  commonest  form  the  curvature  of  the  cor- 
nea is  greater  in  the  vertical  than  in  the  horizontal  mer- 


ASTIGMATISM.  217 

idian,  and,  as  a  result  of  this,  the  rays  which,  diverging 
from  a  given  point,  fall  upon  the  vertical  meridian  of 
the  cornea,  are  brought  to  a.  focus  earlier  than  those 
which  fall  upon  the  horizontal  meridian.  Consequently, 
when  the  eye  is  so  accommodated  that  the  anterior  of 
these  two  foci  falls  upon  the  retina,  the  image  formed 
will  be,  instead  of  a  point,  a  horizontal  line  ;  if  the  pos- 
terior focus  falls  upon  the  retina,  the  image  will  be  a 
vertical  line  (Fig.  27).  Almost  every  eye  is  more  or 
less  astigmatic,  and  none  are  free  from  defects.  One 
constant  defect  consists  in  spheric  aberration,  which 
depends  upon  the  fact  that  rays  falling  upon  the  periph- 


Fig.  27.— Illustrating  astigmatism. 

ery  of  the  lens  are  more  refracted,  and  Brought  to  a 
focus  earlier,  than  those  which  fall  nearer  to  the  prin- 
cipal point.  This  effect  is,  however,  to  a  certain  extent, 
neutralized  by  the  curvature  and  index  of  refraction  of 
the  peripheral  portion  being  less  than  is  the  case  with 
the  more  central  portion  of  the  lens.  The  iris,  too, 
forms  a  diaphragm  which  prevents  light  from  falling  on 
the  periphery  of  the  lens,  and  this  is  of  special  impor- 
tance in  the  case  of  the  more  divergent  rays  which 
reach  the  eye  from  near  objects ;  as  we  have  seen,  the 
iris  contracts  when  near  objects  are  viewed.  Chromatic 
aberration  is  caused  by  dispersion  due  to  the  unequal 
refrangibility  of  rays  of  different  wave-length  ;  those  of 


218  THE  SPECIAL  SENSES. 

shorter  wave-length,  e.  g.,  the  violet  rays,  are  more 
refracted  than  those  of  greater  wave-length,  e.  g.,  the 
red  rays.  Under  ordinary  circumstances,  neither  spheric 
nor  chromatic  aberration  interferes  with  distinct  vision. 
Color  Vision. — White  light  on  analysis  is  found  to 
consist  of  a  mixture  of  rays  of  varying  wave-length. 
When  light  falls  upon  the  retina,  the  resulting  sensa- 
tion varies  with  the  wave-length  of  its  component  rays. 
According  to  the  Young-Helmholtz  theory,  there  are  in 
the  retina  three  substances,  all  of  which  are  to  a  certain 
extent  acted  upon  by  any  ray  of  light,  whatever  its  wave- 
length ;  but  the  readiness  with  which  each  substance 
reacts  to  diiferent  rays  varies.  For  instance,  rays  the 
wave-length  of  which  is  in  the  neighborhood  of 
0.000675  mm.  aifect  one  substance  more  than  the  other 
two,  and  give  rise  to  a  sensation  of  red ;  rays  of  about 
0.000525  mm.  wave-length  produce  the  greatest  effect 
on  the  second  substance,  and  give  rise  to  a  sensation  of 
green  ;  rays  of  0.000430  mm.  wave-length  cause  the 
greatest  change  in  the  third  substance,  and  result  in  a 
sensation  of  violet.  A  sensation  of  yellow  results  from 
the  simultaneous  production  of  red  and  green  sensations 
in  certain  proportion ;  a  sensation  of  orange  is  produced 
by  slightly  increasing  the  red  sensation  and  lessening 
the  green.  Thus  a  host  of  different  color  sensations 
may  be  produced  by  the  fusion  of  the  primary  sensa- 
tions in  varying  proportions.  The  sensation  of  white 
results  from  the  fusion  of  all  three  primary  sensations 
in  definite  proportions;  this  is  what  occurs  when  ordi- 
nary daylight  falls  upon  the  retina,  but  to  produce  this 
result  it  is  not  necessary  that  all  the  rays  of  the  visible 
spectrum  should  enter  the  eye.  Any  two  rays  which 
between  them  excite  all  three  color  sensations  in  the 
right  proportion,  will  give  rise  to  a  sensation  of  white ; 
for  instance,  a  ray  of  the  wave-length  0.000564  mm., 


COLOR  VISION.  219 

when  it  alone  roaches  the  retina,  causes  a  sensation  of 
greenish-yellow  l>y  acting  about  equally  on  the  visual 
substances  concerned  in  red  and  green  sensations  ;  if  to 
this  ray  be  added  one  of  the  wave-length  0.000433 
nun.  which  by  itself  causes  a  sensation  of  violet  by 
acting  to  about  the  same  extent  on  the  third  substance, 
a  sensation  of  white  will  result.  Every  ray  situated 
toward  one  end  of  the  spectrum  has  its  complementary 
ray,  found  toward  the  opposite  end,  combination  with 
which  gives  rise  to  a  sensation  of  white.  Rays  near  the 
middle  of  the  spectrum  which  give  rise  to  a  sensation 
of  green  require  to  be  combined  with  rays  from  both 
ends  of  the  spectrum  in  order  to  cause  a  sensation  of 
white.  A  sensation  of  black  is  caused  by  the  absence 
of  any  stimulus.  There  are  certain  facts  in  color 
vision  which  cannot  be  satisfactorily  explained  on  this 
theory,  and  in  consequence  several  others  have  been 
advanced  ;  to  all  these  there  are,  however,  objections. 
According  to  the  theory  of  Hering,  there  are  six  pri- 
mary color  sensations,  depending  on  anabolic  or  katabo- 
lic  changes  in  three  visual  substances.  In  one  of  these 
substances  katabolic  changes  may  be  excited  by  the  rays 
of  any  part  of  the  visible  spectrum,  and  a  sensation  of 
white  results;  in  the  absence  of  light,  anabolic  changes 
predominate,  and  give  rise  to  a  sensation  of  blackness. 
Another  substance  is  caused  to  break  down  by  the  rays 
of  greater  wave-length,  giving  rise  to  a  sensation  of 
red,  while  it  is  rapidly  built  up  tinder  the  influence  of 
the  rays  of  medium  length,  with  a  resulting  sensation 
of  green.  The  third  substance  suffers  katabolic  changes 
under  the  influence  of  rays  which  thus  produce  sensa- 
tions of  yellow,  and  undergoes  constructive  changes  when 
exposed  to  the  rays  of  shorter  wave-length  which  thus 
produce  a  sensation  of  blue.  When  rays  of  all  wave- 
lengths fall  upon  the  retina,  the  metabolism  of  only  the 


220  THE  SPECIAL  SENSES. 

f  i  white-black  "  substance  is  affected ;  the  other  two  sub- 
stances remain  in  equilibrium.  Orange  sensations  result 
from  the  simultaneous  break-down  of  the  red-green  and 
yellow-blue  substances,  violet  sensations  from  the  simul- 
taneous building  up  of  yellow-blue  and  break-down  of 
red-green  substance. 

Color-blindness  appears  to  depend  upon  the  exist- 
ence in  the  retina  of  the  individual  of  but  two  visual 
substances.  As  a  rule,  those  who  are  color-blind  fail 
to  distinguish  between  red  and  green ;  this  may  be 
explained  on  the  Young-Helmholtz  theory,  by  supposing 
either  the  "  red  substance  "  or  the  "  green  substance  " 
to  be  absent  from  the  retina ;  on  Hering's  theory  by  the 
absence  of  the  "  red-green  substance.77 

When  light  falls  upon  the  retina,  it  affects  both  the 
pigment  epithelial  cells  of  the  outer  layer,  and  the  rods 
and  cones ;  visual  sensation  depends  upon  stimulation 
of  the  latter  elements,  and  it  results  whatever  be  the 
nature  of  the  stimulus.  Pressure  when  applied  to  the 
eyeball  affords  mechanical  stimulation  of  the  retina,  and 
a  visual  sensation  follows.  If  in  the  dark  sudden  pres- 
sure be  applied  to  the  nasal  side  of  the  eyeball,  the 
resulting  sensation  resembles  that  produced  by  a  flash 
of  light  occurring  on  the  opposite  side  of  the  visual  axis, 
and  to  the  subject  it  appears  to  be  the  consequence  of 
such  an  event  taking  place  outside  the  body.  If  the 
experiment  is  made  in  the  light,  the  impression  of  a  dim 
blue  disc  is  given.  The  retina  may  also  be  stimulated 
electrically,  with  the  production  of  visual  sensations. 

Different  parts  of  the  retina  are  not  equally  sensi- 
tive to  light,  and  a  variation  in  the  quality  of  light 
affects  them  differently.  We  can  most  accurately  dis- 
tinguish between  closely  adjacent  points  when  their  im- 
ages fall  upon  the  yellow  spot,  or  macula  lutea;  in  this 
respect  acuteness  of  vision  gradually  diminishes  as  the 


THE  RETINA.  001 

periphery  of  the  retina  is  approached.  The  same  is 
true  in  respect  to  color  vision ;  the  extreme  periphery 
of  the  retina  is  color-blind.  On  the  other  hand,  the 
macula  lutea  is  not  the  part  of  the  retina  that  is  most  sen- 
sitive to  dim  illumination.  Rods  are  absent  from  the 
macula  lutea,  cones  only  being  present ;  as  the  periph- 
ery is  approached,  the  number  of  rods  increases,  the 
number  of  cones  diminishes,  and  before  the  border 
is  reached  the  cones  disappear.  It  seems  probable  that 
the  cones  are  chiefly  concerned  in  acute  vision  and  in 
color  vision,  while  the  rods  minister  to  the  perception 
of  luminosity  without,  perhaps,  affording  a  means  for 
the  appreciation  of  color.  The  rods  contain  a  substance, 
visual  purple,  which  is  absent  from  the  cones,  and  it 
may  be  owing  to  the  presence  of  this  substance  that  the 
rods  are  most  readily  stimulated  by  rays  of  light  of 
short  wave-length,  for  it  is  by  these  that  visual  purple 
is  most  rapidly  bleached.  Visual  purple  is  rendered 
colorless  by  exposure  to  light,  but  during  the  process 
an  intermediate  substance,  a  pigment  called  visual 
yellow,  is  formed.  On  exclusion  of  light,  visual  purple 
again  slowly  appears  in  the  rods,  but  not  in  the  absence 
of  the  layer  of  pigment  epithelium,  which  evidently  ex- 
erts an  influence  on  its  formation.  The  optic  disc,  that 
part  of  the  retina  where  the  fibers  of  the  optic  nerve  leave 
the  eye,  is  devoid  of  rods  and  cones,  and  is  blind.  Of 
this  defect  we  are  unconscious,  until  it  is  pointed  out  to 
us  that,  with  but  one  eye  open,  the  image  of  an  object 
which  falls  upon  this  area  is  unseen.  The  image  of  an 
object  never  falls  simultaneously  upon  the  blind  spots 
of  both  eyes. 

When  light  falls  upon  the  retina,  the  effect  on  con- 
sciousness varies  with  the  intensity  of  the  light,  with 
the  duration  of  the  exposure,  with  the  size  of  the  retinal 
area  illuminated,  and  with  the  condition  of  the  retina. 


222  THE  SPECIAL  SENSES. 

The  excitability  of  the  retina  is  reduced  by  exposure  to 
light ;  it  becomes  fatigued,  and  visual  sensations  are 
less  intense ;  this  probably  also  depends  upon  fatigue 
of  the  central  visual  mechanism.  In  order  to  excite 
visual  sensation,  light  must  be  of  certain  intensity,  this 
intensity  varying  with  the  part  of  the  retina  upon  which 
it  falls.  We  cannot  distinguish  between  the  different 
intensity  of  two  lights,  unless  one  be  brighter  than  the 
other  by  one-hundredth  part,  and,  consequently,  the 
brighter  the  lights,  the  more  difficult  it  is  to  appreciate 
their  different  value.  A  flash  of  light  may  appear  less 
bright  than  a  somewhat  weaker  light  that  lasts  longer. 
A  small  light  may  appear  less  luminous  than  a  larger 
one  which  is  in  reality  of  less  intensity.  Since  the  sen- 
sation outlasts  the  stimulus  by  a  short  period,  a  rapid 
succession  of  stimuli  of  very  short  duration  gives  rise 
to  a  continuous  sensation.  The  survival  of  a  visual 
sensation  after  the  stimulus  has  ceased  is  known  as  a 
positive  after=image.  Negative  after-images  are  fatigue 
phenomena ;  for  instance,  if  after  fixing  the  eye  for  a 
few  moments  upon  a  red  object  it  is  turned  to  a  white 
surface,  there  appears  a  greenish  image  of  this  object ; 
this  is  explained  by  assuming  that  in  the  area  of  the 
retina  upon  which  the  rays  from  the  red  object  fell  the 
visual  substance  upon  which  the  red  rays  take  most 
effect  has  been  used  up  or  rendered  inexcitable  to'  a 
greater  extent  than  either  the  green  or  the  violet  per- 
ceiving elements  ;  consequently,  when  the  whole  retina 
is  subsequently  exposed  to  white  light,  which  excites  all 
three  primary  sensations,  the  two  which  have  not  been 
fatigued  will  predominate,  and  we  experience  a  sensation 
of  greenish-blue.  The  color  of  a  negative  after-image 
is  always  complementary  to  that  of  its  original. 

When  two  objects  the  colors  of  which  are  comple- 
mentary to  one  another  are  placed  in  contact,  the  color 


EXTRINSIC  MUSCLES.  223 

of  each,  more  particularly  along  the  adjacent  edges, 
appears  to  IK-  intensified.  This  may  be  explained  by 
assuming  that  stimulation  of  any  retinal  area  causes 
Hmnltaneous  changes  to  occur  in  neighboring  areas; 
by  some,  these  induced  changes  are  supposed  to  be 
similar  to  those  occurring  in  the  stimulated  area;  by 
others,  they  are  considered  to  be  of  an  opposite  nature. 
A  white  object  on  a  dark  field  looks  larger  than  it 
does  on  a  white  field ;  this  is  called  irradiation,  and 
depends  upon  the  failure  of  the  eye  to  bring  all  the 
rays  to  a  proper  focus,  the  size  of  the  retinal  image 
being  slightly  increased  through  the  formation  of  diffu- 
sion circles  instead  of  points. 

To  each  eyeball  are  attached  three  pairs  of  muscles, 
the  two  members  of  each  pair  being  antagonistic  to 
eaeli  other.  The  movements  of  the  two  eyes  are  asso- 
ciated in  such  a  way  that  their  visual  axes  are  kept 
parallel  to  each  other  when  directed  toward  distant  ob- 
jects. During  accommodation  the  visual  axes  con- 
verge. In  what  is  known  as  the  primary  position  of 
the  eyes,  the  visual  axes  are  parallel,  and,  the  head 
being  erect,  are  directed  toward  a  distant  point  at  their 
own  level.  The  center  of  rotation  of  the  eyeball  lies 
.  13.54  mm.  behind  the  anterior  surface  of  the  cornea  on 
the  optic  axis.  The  optic  axis  docs  not  exactly  corre- 
spond to  the  visual  axis,  but  cuts  the  retina  on  the 
inner  side  of,  and  slightly  above,  the  macula  lutea. 
Dotation  of  the  eyes  from  the  primary  position  to  the 
right  is  caused  by  contraction  of  the  right  external  rec- 
I  tus  muscle  and  left  internal  rectus  ;  horizontal  converg- 
ence is  caused  by  contraction  of  the  two  internal  recti. 
Upward  rotation  is  brought  about  by  the  simultaneous 
contraction  of  the  superior  recti  and  inferior  oblique 
I  muscles ;  downward  rotation,  by  the  simultaneous  con- 
traction of  the  inferior  recti  and  superior  oblique 


224  THE  SPECIAL  SENSES. 

muscles.  More  than  two  muscles  must  act  upon  each 
eye  in  order  to  bring  about  oblique  upward  or  down- 
ward movement;  this  is  accompanied  by  more  or  less 
wheel  movement,  or  rotation  on  the  optic  axis.  The 
voluntary  contraction  of  one  muscle  is  accompanied  by 
inhibition  of  its  antagonist. 

As  long  as,  through  the  associated  movements  of  the 
two  eyes,  the  visual  axes  are  directed  toward  the  same 
point,  an  image  of  this  point  will  fall  upon  the  macula 
lutea  of  each  eye,  and  will  give  rise  to  a  single  sensa- 
tion. The  maculae  luteae  are  not  the  only  areas  of  the 
retinae  simultaneous  stimulation  of  which  gives  rise  to 
a  single  sensation  ;  each  retinal  area,  with  the  exception 
of  those  near  the  nasal  edges  of  the  retinae,  has  a  corre= 
sponding  area  in  the  opposite  retina.  When  the  two 
retinal  images  of  an  object  fall  upon  corresponding  or 
identical  areas,  the  object  appears  single ;  when  the  im- 
ages fall  upon  areas  which  do  not  correspond,  the  object 
appears  to  be  double.  Slight  asymmetry  in  the  position 
of  images  falling  upon  peripheral  areas  of  the  retinae 
does  not  so  readily  cause  diplopia  (double  vision)  as  does 
the  asymmetric  arrangement  of  images  on  the  maculae 
luteae. 

We  first  learn  to  interpret  our  visual  sensations 
through  comparison  with  sensations  provoked  through 
other  channels.  Our  visual  judgment  of  the  size  of  an 
object  is  formed  by  comparing  the  sensation  which  it 
excites  with  those  produced  by  other  objects  with  which 
we  are  familiar,  and  if  the  object  be  large,  by  the  angle 
through  which  the  eye  must  be  moved  in  order  to  cover 
its  surface.  The  movements  of  the  eye  are  estimated 
partly  through  the  intensity  of  the  effort  expended  in 
causing  the  contraction  of  the  ocular  muscles,  and  partly 
through  the  muscular  sensation  resulting  from  their 
contraction.  The  distance  of  an  object  may  be  much 


HEARING.  225 

more  accurately  determined  by  using  both  eyes  than  by 
ii.-ing  only  one  ;  in  the  case  of  a  near  object,  the  degrees 
of  accommodation  and  of  convergence  are  important 
aids  to  judgment  of  distance.  It  is  difficult  to  form  an 
idea  of  the  shape  of  an  unfamiliar  solid  object  by 
m rans  of  one  eye,  but  since,  when  both  eyes  are  used, 
it  is  viewed  from  two  points,  the  retinal  images  differ 
slightly,  and  we  are  enabled  to  appreciate  its  depth. 

HEARING. 

Sound-waves  that  enter  the  external  auditory  meatus 
cause  vibration  of  the  tympanic  membrane,  and  are 
transmitted  through  the  chain  of  ossicles,  which  vibrate 
as  a  whole,  to  the  perilymph  of  the  internal  ear.  The 
vibration  of  the  perilymph  is  transmitted  to  the  endo- 
lymph  of  the  membranous  labyrinth,  and  in  some  way 
takes  effect  on  the  terminations  of  the  nerve-fibers  of  the 
auditory  branch  of  the  eighth  cranial  nerve.  Pressure 
on  the  two  sides  of  the  tympanic  membrane  is  equalized 
by  the  communication  which  exists  between  the  middle 
ear  and  the  pharynx  by  means  of  the  Eustachian  tube ; 
uneven  pressure  would  interfere  with  the  vibration  of 
the  membrane. 

The  vibrations  which  give  rise  to  a  musical  sound  are 
rhythmic  ;  a  noise  results  from  arhythmic  vibrations. 
Sounds  vary  in  intensity,  or  loudncss,  in  pitch,  and  in 
quality.  Intensity  depends  upon  the  amplitude  of  the 
vibration  ;  pitch,  upon  the  rate  of  vibration.  A  single 
sound  emitted  by  a  musical  instrument  is  usually  not 
simple,  but  compound,  and  this  depends  upon  the  ad- 
mixture of  overtones  with  the  fundamental  tone.  The 
same  note  produced  by  different  instruments  differs  in 
quality,  owing  to  variation  in  the  number  and  intensity 
of  accompanying  overtones.  When  two  sounds  occur 
15 


226  THE  SPECIAL  SENSES. 

simultaneously,  the  vibrations  upon  which  they  depend 
do  not  reach  the  ear  separately,  but  are  fused,  and  form 
a  compound  wave ;  nevertheless,  we  are  capable  of 
analyzing  a  complex  sound.  The  ear  probably  contains 
a  system  of  resonators,  which,  like  the  strings  of  a  harp 
or  other  instrument,  are  caused  to  vibrate  when  sub- 
jected to  the  influence  of  sound-waves,  each  resonator 
responding  to  a  tone  of  definite  pitch.  The  basilar 
membrane  of  the  cochlea,  with  its  thousands  of  radial 
fibers  of  different  lengths,  perhaps  serves  as  a  system 
of  resonators  in  the  analysis  of  sounds,  the  vibration  of 
each  fiber  being  communicated,  through  the  organ  of 
Corti,  to  a  particular  nerve-fiber  of  the  auditory  nerve. 
Our  aural  judgments  are  much  less  exact  than  our 
visual  judgments,  and  even  by  the  use  of  both  ears  it. 
is  difficult  to  determine  whence  a  sound  reaches  us. 
This  is  especially  true  of  sounds  which  emanate  from  a 
point  in  the  median  vertical  plane.  It  is  less  difficult 
to  locate  sounds  whose  source  of  origin  is  lateral  to  the 
head,  for,  in  this  case,  the  intensity,  and  perhaps  the 
quality  of  the  sound,  as  it  reaches  the  two  ears  varies. 

SMELL. 

The  true  olfactory  mucous  membrane  is  very  limited 
in  extent,  and  is  confined  to  that  portion  of  the  nasal 
mucous  membrane  which  covers  the  medial  surface  of 
the  superior  turbinated  bone,  and  the  corresponding 
area  of  the  septum.  Here  are  situated  cells  which 
give  off  the  fibers  which  constitute  the  olfactory  nerve, 
and  end  in  the  olfactory  bulb.  The  air  as  it  is  inspired 
does  not  pass  over  this  area,  but  gases  and  particles  of 
odorous  substances  which  enter  the  nose  reach  the 
olfactory  mucous  membrane  by  diffusion.  Odorous 
substances  may  excite  a  sensation  of  smell  when  intro- 


QUESTIONS.  227 

duced  into  the  nostrils  in  solution  in  normal  saline,  but 
not  in  distilled  water,  which  probably  injures  the  olfac- 
tory cells. 

TASTE. 

Not  the  whole  of  the  oral  mucous  membrane  is  sen- 
sitive to  sapid  substances  ;  the  taste  organs  are  confined 
to  the  back,  the  tip,  and  the  edges  of  the  tongue,  and 
to  the  palate  and  the  pillars  of  the  fauces ;  their  distri- 
bution, however,  varies  considerably  in  different  indi- 
viduals. The  taste-buds,  which  are  found  on  the  sides 
of  the  circumvallate  papilla?,  and  on  the  fungi  form 
papilla?,  are  supposed  to  serve  as  end-organs  of  taste, 
but  probably  there  are  others.  The  back  of  the  tongue 
is  most  sensitive  to  bitter  substances  ;  the  tip  and  sides, 
to  sweet  substances.  The  other  tastes  are  acid  and  salt ; 
flavors  are  appreciated  by  the  olfactory  cells,  and  are 
not  true  tastes.  Nerve-fibers  which  are  concerned  in 
taste  are  supplied  to  the  back  of  the  tongue  by  the 
glossopharyngeal  nerve,  and  to  the  anterior  two-thirds 
by  the  lingual,  but  the  path  by  which  these  fibers  enter 
the  medulla  is  uncertain. 


QUESTIONS  FOR  CHAPTER  X. 

Can  parallel  and  divergent  rays  of  light  which  happen  to  fall 
upon  the  eye  be  simultaneously  focused  on  the  retina? 

During  accommodation,  where  are  parallel  rays  brought  to  a 
focus  ? 

What  sort  of  lens  must  be  used  for  the  correction  of  myopia? 

What  sort  of  lens  is  needed  after  removal  of  the  lens  from  the 
eye? 

To  what  extent  is  vision  interfered  with  by  the  application  of 
atropin  ? 

How  do  we  know  that  light  does  not  stimulate  the  fibers  of  the 
optic  nerve  ? 


228  THE  SPECIAL  SENSES. 

Why,  when  accommodation  is  relaxed,  does  a  near  object  appear 
to  be  double  ? 

Why  is  vi'sion  indistinct  when  the  eye  is  immersed  in  water  ? 

Why  do  hypermetropic  eves  tire  more  readily  than  myopic  eyes? 

What  effect  on  the  eye  has  division  of  the  cervical  sympathetic 
nerve  ? 

When  the  internal  rectus  muscle  of  one  eye  is  paralyzed,  the 
eyeball  will  be  rotated  outward,  owing  to  the  unresisted  tonic 
contraction  of  the  external  rectus.  Why,  under  these  circum- 
stances, should  turning  the  opposite  eye  outward  cause  the  injured 
eye  to  return  to  the  primary  position  ? 

Why  does  the  application  of  pressure  to  one  side  of  the  eyeball 
cause  diplopia  ? 

If  sound-waves  reach  the  retina,  why  do  they  not  result  in 
visual  sensation  ? 


INDEX. 


ABDUCENS,  198 
Aberration,  217 
Absorption  of  cane-sugar,  80 

of  egg-albumen,  92 

of  fat,  94 

of  native  proteids,  83,  95 

of  peptones,  90, 91 

of  starch,  80 

of  water,  95 

Accelerator  center,  47,  49 
Accessory  nerve,  71, 171,  200 
Accommodation,  196,  213,  214, 

223 

Achroodextrin,  79 
Acid  albumin,  84 

amido-,  85,  111,  112 

benzoic,  112 

butyric,  81 

carbamic,  110 

fatty,  93, 94 

hippuric,  112,  128 

hydrochloric,  79,  80,  84,  87 

lactic,  81, 94, 106,  110 

phosphocarnic,  69,  158 

phosphoric,  128 

sulphuric,  123,  128 

uric,  111,127,  128,  132 
Acromegaly,  116 
Action  current,  156 
Addison's  disease,  116 
Adrenal  bodies,  116 

extract,  149 

Afferent  nerve-fibers,  164 
After-image,  222 


Agglutinating      property      of 

blood,    34 
Albumin,  14,  159 

coagulation  temperature  of, 

21 

Albuminate,  84 
Albuminoids,  89 
Albumoses,  14,  25,  85 
Alcohol,  51,81,92 
Alexia,  204 
Alkali  albumin,  84, 92 
Alkalinity  of  blood,  20,  123 
Amido-acids,  85,  95,  111,  112 
Ammonia,  21,48,  123 
Ammonium  salts,  110,  111 
Amylopsin,  79 
Anabolism,  17 
Anaerobic  contraction,  69 
Anemia,  124     »' 
Animal  heat,  141 
Antagonistic    muscles,    inhibi- 
tion of,  166,  193,  224 
Anterolateral  ascending  tract, 

178,  205 
Aorta,  44,  45 
Apesthesia,  204 
Aphasia,  204,  205 
Apnea,  74 

Aqueous  humor,  210 
Arcuate  fibers,  174 
Areas,  association,  204 

auditory,  204 

motor  cortical,  192,  202 

retinal,  224 


229 


230 


INDEX. 


Areas,  sensory  cortical,  188, 202 

visual,  185,  202 
Arterialization  of  blood,  67 
Arteries,  blood-flow  in,  56 

blood-pressure  in,  46,  48,  50, 

51 
Arterioles,  46 

direct  stimulation  of,  116 

innervation  of,  52 
Asphyxia,  74 

Aspiration,  thoracic,  58,  59 
Assimilation,  113 
Association  areas,  204 

fibers,  205 
Astigmatism,  215 
Atropin,  98, 137,  139,  215 
Auditory  area,  204 

nerve,  182,  226 
Auerbach's  plexus,  101,  172 
Augmentor  center,  47,  49,  50 

nerve,  course  of,  49 
Autonomic  nerve-fibers,  171 


BACTERIA,  33,  78,  81,  83,  87, 95 
Bacteriolysins,  34 
Baths,  144 
Benzoic  acid,  112 
Bile,  87,  94,  95 

pigments,  95 

salts,  94,  95 
Biological   test   for   source   of 

suspected  blood,   35 
Bioplasm,  11 
Bladder,  gall-,  100 

urinary,  134 
Blindness,  188,  202 
Blood,  19 

adaptation  of,  33 

agglutinating  property  of,  34 

alkalinity  of,  20,  123 

biological  test  for,  35 

circulation  of,  39 

coagulation  of,  21 

color  of,  32 

defibrinated,  22,  25,  26 

functions  of,  19 

reaction  of,  21,  123 


Blood,  salted,  22 
venosity  of,  48 
Blood-cells,  19 
red,  19,31 

functions  of,  20 
white,  19,24,32,  112 

functions  of,  33 
Blood-flow,  arterial,  56 

capillary,  45,  56 
Blood-plasma,  20 
dextrose  in,  108 
Blood-platelets,  19,  32 
Blood-pressure,  arterial,  46,  48, 

50,51 

influence  of  respiration  on,  58 
intracapillary,  36 

intravenous  negative,  59 
respiratory  variation  of,  59 
regulation  of,  48,  51,  52 
Blood-supply,  coronary,  50 

during  activity,  56,  69 
Brachium  conjunctivum,  178, 

206 
Bundle,  Meynert's,  retroflexed, 

188 
posterior  longitudinal,    180, 

184,  185, 198 
solitary,  180 
Burdaclvs  tract,  174 
Butyric  acid,  81 


CALCIUM,  25,  123 
Calorie,  122 
Cane-sugar,  13,  16 

digestion  of,  80 

in  urine,  80 
Capillaries,  blood-flow  in,  45, 56 

blood-pressure  in,  36,  131 

exchange  of  gases  in,  68 

permeability  of,  35 

renal,  129 

Capsule,  internal,  192,  196,  203 
Carbamic  acid,  110 
Carbohydrates,  13 

bacterial  decomposition   of, 
81,87 

digestion  of,  77,  83 


INDEX. 


231 


Carbohydrates,    potential    en- 

cr<;y  of,  122 
Carbon  dioxid,  69 

elimination  of,  68, 127 
in  blood,  68 

equilibrium,  118 

monoxid,  32 

hemoglobin,  32 
Cardinal  points,  212 
Cardio-accelerator  center,  47, 

49 
Cardio-augmentor   center,   47, 

49 
Cardio-inhibitory    center,    47- 

51, 116 

Casein,  89,  138 
Caseinogen,  89,  138 
Cellulose,  16,  78,  81,  88,  121 
Cerebellum,  174,  178,  190,  205 
Cerebral  hemispheres,  removal 

of,  194,  203 
Cerebrum,  202 
Chemotropism,  33 
Chloroform,  48,  51,  55 
Cholesterin,  17,  31,  32,  95,  137 
Cholic  acid,  95 
Chorda  tympani,  55,  56,  97 
Chromatic  aberration,  217 
Chyle,  105 
Ciliary  muscle,  211,  213,  214 

nerves,  215 

Clarke's  column,  178,  193 
Coal-gas  poisoning,  32 
Cochlea,  226 
Cochlear  nerve,  182 
Cold,  influence  on  circulation, 

51,  130,  142 

on  metabolism,  122,  142 
on  renal  secretion,  130 
on  respiration,  73,  145 
on  vasoconstrictor  center, 

51,  130,  142 

Cold-blooded  animals,  141 
Cold-nerves,  140 
Collagen,  90 
Collaterals,  157, 164 
Color-blindness,  219 
Color-vision,  218-220 


Colostrum,  138 
Complement,  34 
Conductivity  of  muscle,  148 

of  nerve,  152,  157,  158 
Cones,  retinal,  185,  221 
Conjugated  sulphates,  87,  128 
Constipation,  88 
Constrictor  center.     See  Vaso- 
constrictor center. 
Contraction,  148 
isometric,  150 
isotonic,  150 
law  of,  152 

Pfliiger's,  152 
maximal,  149 
tetanic,  151 
voluntary,  150 
Contrast,  223 
Convergence,  214,  223 
Coordination,  203,  204,  206 
Cornea,  210 

Coronary  blood-supply,  50 
Corpora  geniculata,  182,  185 
quadrigemina,  174,  178,  ivJ. 

190,  198,  202 
Corpus  callosum,  205 
marnillare,  188 
restiforme,  174,178 
Cortex  cerebri,  association  areas 

of,  204 

inhibition  by,  193 
motor  areas  of,  192,  202 
sensory  areas  of,  188,  202 
Coughing,  73 
Cranial  nerves,  eighth,  182, 188, 

226 

eleventh,  71,  171,200 
fifth,  48,  73,  96,  99,  184, 

196 

first,  188 
fourth,  196 
ninth,  49,  96,99,  171,  180, 

182,  198,  227 
second,  185 
seventh,  56,  171,198 
sixth,  198 

tenth,  43,  47,  48,  72,  74, 
99, 171,  180,  200 


232 


INDEX. 


Cranial  nerves,  third,  171, 196, 

202, 214 
twelfth,  200 

Creatin,  111,  112,  128,  158 
Creatinin,  111,  128       • 
Cretinism,  115 
Cristse  ampullares,  207 
Curari,  145,  148 
Current,  action,  156 

constant,  151,  167 

demarcation,  155 

induced,  151,  167 
Cycle,  cardiac,  40,  42 


DEAFNESS,  204 
Decussation,  pyramidal,  193 

sensory,  174 
Defecation,  102 

Degeneration   of   nerve-fibers, 
156 

of  spinal  nerve-roots,    176, 
178 

reaction  of,  155,  167 
Deglutition,  49,  98 

influence  of,  on  respiration, 

73,99 

Dehydrolysis,  18, 106 
Demarcation  current,  155 
Depressor  nerve,  51,  116 
Dextrin,  16,  17 
Dextrose,  13, 15,  18 

formation  of,  from  proteid, 
107,  109, 119 

metabolism  of,  105 
Diabetes  mellitus,  107,  108 

pancreatic,  108 
Diapedesis,  33 
Diaphragm,  63 
Dicrotic  pulse,  58 
Diet,  carbohydrate,  67,  120 

fatty,  122 

ideal,  121 

influence  of,  on  respiratory 
quotient,  67 

milk,  88,  124,  138 

mixed,  120 

vegetable,  112, 123, 129 


Digestion,  77 

of  albuminoids,  90 

of  carbohydrates,  77,  82 

of  fat,  93 

of  nucleoproteids,  88 

of  proteids,  83,91 
Diplopia,  224 
Diuretics,  133 
Dyspnea,  71,  74 

cardiac,  72 

hemorrhagic,  71 

influence    on    cardio-inhibi- 

tory  center,  48 
on  vasoconstrictor  center, 
51 

CO2-,  72 

O-,  72 


EAR,  225 

Efferent  nerve-fibers,  164 
Egg-albumen,  92 
Elasticity  of  aorta,  39 
of  lungs,  65 
of  muscle,  148 
Elastin,  90 
Electrolytes,  29 
Electrotonus,  153 
Emmetropia,  216 
Emotions,     influence     of,    on 

heart,  49 
on  movements  of  stomach, 

100 

on  respiration,  73 
on  secretion  of  milk,  138 
on  secretion  of  saliva,  97  • 
Emulsification,  93 
Enamel,  destruction  of,  81 
Energy,  117,  121, 141 
Enzymes,  characteristics  of,  23 
Epinephrin,  117 
Equilibrium,  184,  192,  205,  207 
carbon, 118 
nitrogenous,  118,  120 
Erythrocytes,  19,  31 

functions  of,  20 
Erythrodextrin,  79 
Esophagus,  99 


INDEX. 


233 


Evaporation  of  sweat,  135, 143 
Excretion,  127 

Exercise,  influence  of,  on  heart- 
beat, 50 
on  metabolism,  106,  113, 

122,  128 

on  respiration,  72 
on  respiratory  quotient,  67 
Extracts,  adrenal,  117,  149 
Eye,  reduced,  211 

muscles  of,  196, 198,  223,  224 


FACIAL  nerve,  56,  171,  198 
Fallopian  tubes,  170 
Fat,  16 

digestion  of,  93 

in  milk,  138 

metabolism  of,  107,  108,  118 

potential  energy  of,  122 
Fatigue  of  muscle,  149 

of  nerve,  158 

of  retina,  222 
Fatty  acids,  93,94 

diet,  122 
Feces,  87, 102 

Ferments,  characteristics  of,  23 
Fever,  141 
Fibrin,  22 

Fibrin-ferment,  24,  25,  32 
Fibrinogen,  22 

coagulation  temperature  of, 
21 

solubility  of,  14 
Fillet,  174, 180, 184 

descending  fibers  of,  198,  200 

lateral,  182 

Filtration  of  urine,  131, 133 
Fornix,  188 
Freezing- point,  depression  of, 

29 
Fruit-sugar,  15 


GANGLION,  Gasserian,  184,  215 
posterior  root,  156, 162 
spiral,  182 


Ganglion,  superior  cervical 
sympathetic,  52,  56,  97, 
137,  215 

sympathetic,  168 
Gastric  juice,  84 

secretion  of,  99 
Gelatin,  90, 121 
Geniculate  bodies,  182,185 
Globulicidal  action,  26 
Glossopharyngeal  nerve,  49, 73, 

99,  182,  198,  227 
Glycerin,  93 
Glycocol,  95,  111,  113 
Glycogen,  16,  105,  112,  118 
Glycoses,  16 
Glycosuria,  107 
Goll's  tract,  174 
Gowers'  tract,  178 
Gram-molecule,  29 
Grape-sugar,  13,  15 


HEARING,  225 
Heart,  39 

acceleration  of,  47,  49 

beat,  40 

contraction-volume  of,  47 

cycle,  40,  42 

dilatation  of,  47,  50 

during  starvation,  119 

frequency,  41,  43 

influence  of  blood  on,  50 
of  blood-pressure  on,  50 

inhibition  of,  48 

innervation  of,  43,  47,  48 

output  of,  47,  50 

residual  blood  in,  47 

sounds,  43,  44 

valves  of,  39-43,  58 
Heat,  animal,  139 

influence  of,  on   circulation, 
141 

loss  of,  139,  141 

production,  139 
Heat-nerves,  140,  172 
Hematin,  31 
Hemispheres,  cerebral,  removal 

of,  202,  203 


234 


INDEX. 


Hemochromogen,  31 
Hemoglobin,  31,  68,  95 
Hemolysins,  34 
Hemophilia,  21 
Hibernation,  145 
Hippocampus,  188 
Hippuric  acid,  112,  128 
Hydremic  plethora,  133 
Hydrochloric  acid,  79,  84,  87 
action    of,    on    carbohy- 
drates, 80 

Hydrolysis,  18,  78,  84,  93 
Hypermetropia,  216 
Hyperpnea,  19 
Hypoglossal  nerve,  200 


IMMUNE  body,  34 
Indol,  87 

Induced  current,  151 
Inhibition,  cortical,  193 

of  antagonistic  muscles,  166, 
193,  224 

of  the  heart,  48 
Inorganic  salts  in  diet,  122 

uses  of,  123 

Insensible  perspiration,  135 
Internal  capsule,  174,  192 

secretion,  108, 114 
Interpleural  pressure,  64 
Intestinal  epithelium,   80,   81, 
92,94 

juice,  80,  81 

movements,  101 
Intracapillary  pressure,  36 
Invertin,  80 
lodin,  79 
lodothyrin,  115 
Ions,  29 
Iron  in  food,  124 

in  hemoglobin,  31,  96 

in  milk,  138 
Irradiation,  223 
Irritability,  12 

influence  of  constant  current 
on, 151 

myotatic,  166 
Isomaltose,  79 


Isometric  contraction  of  mus- 
cle, 150 

Isotonic  contraction  of  muscle, 

150 
solutions,  29 


KATABOLISM,  17 
Keratin,  90 

Kidneys,  excretion  of  sugar  by, 
107 

removal  of,  110 

secretion  by,  129 
Knee-jerk,  166 
Kreatin,  111,  112,  128,  158 
Kreatinin,  111,  128 


LACRIMAL  glands,  innervation 

of,  171 

Lactation,  137 
Lactic  acid,  81,  94,  106,  110 
Lactose,  16,  80,  138 
Language,  204 
Laryngeal  nerves,  73,  99 
Lecithin,  17,31,32,95 
Lemniscus,  174,  180,  184,  198, 

200 

Lens,  210 
Leucin,  85,  111 
Leukemia,  112 
Leukocytes,  19,  25,  32,  112 
Levulose,  15,  80,  108 
Light-reflex,  202 
Lingual  nerve,  227 
Liver,  capillaries  of,  35 

disease  of,  111 

formation  of  conjugated  sul- 
phates by,  87 
of  urea  by,  110 

glycogenic  function  of,  105 

removal  of,  110 
Locomotor  ataxia,  204 
Lungs,  collapse  of,  58,  65,  72 

function  of,  63 

inflation  of,  58,  64,  72 

influence  of,  on  coagulation, 
25 


ixnr.x. 


235 


Lungs,  ventilation  of,  63 
Lymph,  19,  35,  51) 

factors  which  control  flow  of, 

36 
Lymphatic  circulation,  105 


MACULA  acustica,  207 
lutea,  185,  193,  220 
Maltase,  23 
Maltose,  16,  78 
Malt-sugar,  16,  78 
Mastication,  77,  96 

muscles  of,  198 
Metabolism,  17 

abnormal,  108,  115,  116 

acids  formed  in,  122,  128 

carbohydrate,  105 

during  starvation,  118 

muscular,  106,  108,  114,  142 

of  fat,  108 

proteid,  109,  119 
Methemoglobin,  32 
Micturition,  134 
Milk,  composition  of,  138 

curdling  of,  89 

diet,  88, 124,  138 

secretion  of,  137 
Milk-sugar,  15,  80,  138 
Motor  cortical  areas,  192 
Mucin,  95 
Muscle,  147 

cardiac,  147, 149 

ciliary,  211 

composition  of,  158 

contraction  of,  148,  150 

elasticity  of,  148 

extensibility  of,  148 

injury  to,  155 

irritability  of,  147,  151 

isometric  contraction  of,  150 

isotonic  contraction  of,  150 

latent  period  of,  148 

plain,  147 
Muscles,  inspiratory,  63,  70 

of  eyeball,  196, 198,  223 

of  mastication,  198 
Muscle-sense,  173,  176,  204 


Muscle-spindles,  173 
Muscular  metabolism,  106,  108, 

114, 142 
tone,  117,  147,167 

exaggeration  of,  196 
work,  122 

influence  of,  on  heart-beat, 

50 

on  metabolism,  106 
on  respiration,  72 
on  respiratory  quotient, 

67 

Myoglobulin,  159 
Myopia,  215 
Myosin,  158 
Myosinogen,  159 
Myotatic  irritability,  166 
Myxedema,  115 


NEGATIVE  variation,  156 
Nerve-fibers,  156 
Nerve-impulse,  148 
Nerve-roots,  160 

division  of,  204 
Nerves,  afferent,  164,  172 

afferent  visceral,  173 

cold-,  142,  172 

conductivity  of,  152,  158 

cutaneous,  152,  157 

efferent,  164.' 

heat-,  142,  172 

muscle-sense,  173 

pain,  172 

post-ganglionic,  49,  168 

pre-ganglionic,  49,  168 

pressure,  172 

regeneration  of,  156 

sympathetic,  167,  174 
Nervous  system,  160 

during  starvation,  119 
Neurone,  156 
Nitrogenous  equilibrium,    118, 

120 

Normal  salt  solution,  26 
Nuclein,  13,88,  111 
Nucleo-albumin,  88,  138 


236 


INDEX. 


Nucleoproteids,  12,  21,  25,  88, 

111 
Nucleus  alae  cinerese,  180 

ambiguus,  198 

cochlear,  182 

cuneatus,  174 

Deiters',  206 

gracilis,  174 

habenuke,  188 

vestibular,  182,  190,  206,  207 
Nutrition,  117 


OCCIPITAL  lobe,  188 

Oculomotor  nerve,  196 

(Esophagus,   97.      See    Esoph- 
agus. 

Olein,  17,  109,  138 

Olfactory  nerve,  188,  226 

Olive,  inferior,  190 
superior,  182 

Optic  disc,  221 
nerve,  184 
thalamus,  168,  188,  206 

Osmosis,  26,  131 

Oxalic  acid,  112 

Oxygen  in  blood,  67 

Oxyhemoglobin,  68,  69,  70 


PAIN,  180 

referred,  168 
Palmitin,  17,  138 
Pancreas,  disease  of,  108 

removal  of,  108 
Pancreatic  diabetes,  108 

digestion   of  carbohydrates, 

79 

of  fat,  93 
of  proteids,  84 
Paralysis,  106,  203 
Paralytic  secretion,  98 
Paramyosinogen,  159 
Pepsin,  84 

Peptones,  14,  84,  90,  100 
Peripheral  resistance,  45,   50, 

51 
Peristalsis,  100, 101,  171 


Permeability  of  capillary  wall, 
35 

of  membranes,  27,  30 

of  renal  epithelium,  131,  133 
Pfliiger's   law   of   contraction, 

152 

Phagocytosis,  33 
Phenol,  87 

Phosphates  in  urine,  128,  129 
Phosphocarnic  acid,  70,  158 
Phosphoric  acid,  128 
Phrenic  nerve,  71 
Physiology,  definition  of,  11 
Physostigmin,  215 
Pialyn,  93 
Pigments,  bile,  95 

urinary,  128 
Pilocarpin,  98,  137 
Pilomo tor  nerve-fibers,  171 
Pituitary  body,  116 
Plain  muscle,  147 
Plasma,  20 

dextrose  in  ,J.08 
Pneumogastric  nerve,   43,  47, 

48,72,74,99,  171,180,200 
Portal  circulation,  105 

vein,  dilatation  of,  46 

innervation  of,  55 
Posterior  longitudinal  bundle, 

180,  184,  185,  190,  198 
Post-ganglionic  nerve-fibers,  49, 

168 

Precipitins,  35 
Pre-ganglionic  nerve-fibers,  49, 

168 

Presbyopia,  206 
Pressure,  arterial,  45,  48 

atmospheric,  63 

blood,  45 

intravenous  negative,  59 
respiratory  variation  of,  59 

interpleural,  64 

intracapillary,  36 

intrapulmonary,  64 

negative,  64 

osmotic,  26,  36,  131 

partial,  67 
Pressure-sense,  176 


INDKX. 


237 


Progression,  205 
Proteid  metabolism,  109,  119 
Proteids,  absorption  of,  83,  90, 
91,  95 

bacterial    decomposition  of, 
87 

characteristics  of,  13 

composition  of,  13 

digestion  of,  83 

formation  of  dextrose   from, 

107,  108,  118 
of  fat  from,  109 
of  glycogen  from,  107 

in  urine,  133 

osmotic  pressure  of,  131 

solubility  of,  14,  123 

tissue,  113 
Proteoses,  14,  84,  90 
Protoplasm,  11 

assimilation  of,  12 

conductivity  of,  12 

contractility  of,  12 

irritability  of,  12 

nutrition  of,  12 

reproduction  of,  12 
Pseudo-nuclein,  88 
Pseudo-reflex,  157 
Ptyalin,  78 
Pulse,  56 

dicrotic,  58 

form  of,  57 

variation  of,  57 

venous,  59 

Puncture  diabetes,  107 
Pupil,  constriction  of,  196,  214 

dilatation  of,  215 

reflexes  of,  202 
Pupillo-dilator  fibers,  171 
Pyramidal  cells,  192 

decussaj,ion,  193 

tracts,  192,  193 
Pyramids,  decussation  of,  193 

section  of,  196 


KAMI  communicantes,  167 
Reaction,  influence  of,  on  pep- 
sin, 85 


Reaction,     influence     of,     on 

ptyalin,  79 
on  rennin,  89 

of  blood-plasma,  21,  123 

of  degeneration,  155,  167 

of  sweat,  135 

of  urine,  129,  132 
Recurrent  sensibility,  165 
Red  blood-cells,  19,  31 
functions  of,  20 

nucleus,  192,  206 
Reduced  eye,  211 
Referred  pain,  168 
Reflex  action,  48 

arc,  164 

centers,  167 

pseudo-,  157 
Reflexes,  165 

special,  167 

tendon, 166 
Refraction,  210 
Regeneration   of   nerve-fibers, 

156 
Renal  nerves,  130 

secretion,  129 

tubules,  132 

vessels,  129 
Rennin,  89 
Residual  air,  66 

blood,  47 
Respiration,  external,  66 

influence   of    blood-pressure 

on,  58,  65 
of  exercise  on,  72 
of  venous  blood  on,  71 

internal,  68 

types  of,  65 
Respiratory  capacity,  66 

center,  70 

muscles,  63 

3uotient,  66 
lythm,  70 
surface,  66 
volumes,  65 

Restiform  body,  174,  178 
Retina,  210,  212,  220 
Retinal  areas,  224 
cones,  185,  221 


238 


INDEX. 


Retinal  ganglion-cells,  185 

rods,  185,  221 
Rhythm,  cardiac,  143 

intestinal,  101 

of  ureters,  134 

respiratory,  70 
Rigor  mortis,  158 
Rods  of  retina,  185,  221 


SACRAL  nerves,  171 
Saline  diuretics,  133 
Saliva,  78,  83,  96 

secretion  of,  96,  98 
Salivary  glands,  96 

innervatioii  of ,  171 
Sebaceous  glands,  137 
Secretion,  internal,  108,  114 

of  bile,  114 

of  gastric  juice,  99 

of  milk,  137 

of  pancreatic  juice,  100 

of  saliva,  96,  98 

of  sweat,  136 

of  urine,  129 

paralytic,  98 

Secretory  nerves,  gastric,  99 
pancreatic,  100 
salivary,  96,  97 
sweat,  136 

Semicircular  canals,  205,  207 
Serum,  21 

globulicidal  action  of,  26 
Serum-albumin,  14 

coagulation  temperature  of, 
21 

solubility  of,  14 
Serum-globulin,  14 

coagulation  temperature  of, 
21 

solubility  of,  14 
Shivering,  142 
Short  sight,  215 
Skatol,  87 
Smell,  226 
Sneezing,  73 
Soap, 93 
Solubility  of  proteids,  14,  123 


Sound, 225 

Special  senses,  210 

Spectra,  31 

Speech  center,  204,  205 

Spheric  aberration,  217 

Spinal  animal,  165 

cord,  160 

division  of,  55,  71,  131 

nerve-roots,  160 
Spleen,  innervation  of,  170 
Starch,  13,  16,  78 
Starvation,  67,  107,  108,  118, 

120,  121 
Steapsin,  93 
Stearin,  17,  93,  109,  138 
Stereochemical  formulse,  15 
Stimulation,  unipolar,  law  of, 

154 
Stimuli,  12, 147, 151 

minimal,  149 
Stomach,  innervation  of,  100, 

170 

Striae  acusticae,  182 
Strychnin,  137 
Substantia  gelatinosa,  184 
Succus  entericus,  80,  81,  87 
Sulphuric  acid,  123,  128 
Superior  cervical  sympathetic 

ganglion,  52,  56,  97,  137,  215 
Sweat,  134 
Sweat-gland,    innervation    of, 

171 

Sympathetic  ganglia,   49,   52, 
168 

nerve-fibers,  167-171 

system,  167 


TABES,  204 

Taste,  227 

Taurin,  95 

Temperature,  axillary,  144 

coagulation,  21,  159 

influence  on  cardio-augmen- 

tor  center,  50 
on  respiration,  72 

regulation  of,  141 
Temperature-sense,  180 


239 


Test,  biological,  for  suspected 
blood,  :i") 

Tetanus,  151 

Thalamus,  optic,  174,  188,  206 

Thermogenic  centers,  143 

Thyroid,  115 

influence  of,  on  circulation, 
115 

Thyroiodin,  115 

Tissue  proteid,  113 

Tone,  exaggeration  of,  116 
of  cardio-augmentor  center, 

49 
of  cardio-inhibitory    center, 

48 

of  plain  muscle,  147 
of  skeletal  muscle,  117,  166 
of  vasoconstrictor  center,  51 
vascular,  52,  55.  116 

Tracts,    ariterolateral   ascend- 
ing, 178,  204 
ascending  spinal,  173 
descending  spinal,  176,  190 
direct  cerebellar,  178,  205 
dorsolateral,  174,  205 
dorsomedian,  174,  205 
pyramidal,  176,  192,  193 

Transfusion,  25 

Trapezium,  182 

Trochlear  nerve,  196 

Trypsin,  85 

Tympanum,  225 

Tyrosin,  85,  111 


UNCUS,  188 

Unipolar  stimulation,  law  of, 
154 

Urari,  145,  148 

Urea,  122 

amount  of,  127 
excretion  of,  132,  135 
formation  of,  109,  111 

Uremia,  135 

Ureter,  133 

Uric  acid,  111,  128 
amount  of,  127 
excretion  of,  132 


Urine,  albumin  in,  133 
amount  of,  129 
cane-sugar  in,  80 
composition  of,  127 
concentration  of,  132 
dextrose  in,  107 
filtration  of,  131,  133 
maltose  in,  80 
peptones  in,  92 
reaction  of,  129,  132 
specific  gravity  of,  129 
urea  in,  110 

Urobilin,  96 

Uterus,  innervation  of,  170 


VAGUS  nerve,  43,  47,  48,  72, 

74,  99,  117,  171,  180,  200 
Valves,  cardiac,  39,  41,  43,  44, 

58 

of  veins,  59 

Vasoconstrictor  center,  51,  107 
influence  of  afferent  nerves 

on,  51 

of  blood  on,  51 
of  blood-pressure  on,  51 
of  depressor   nerve   on, 

51 

of  drugs  on,  51,  55 
of  emotions  on,  52 
tone  of,  51' 
nerve-fibers,   course  of,   52, 

55,  97 

cutaneous,  136 
renal,  130 

Vasodilator  centers,  55 
nerve-fibers,  55,  97 

renal,  131 

Vegetable  diet,  112,  123,  129 
Veins,  blood-flow  in,  45,  56,  57, 

59 
blood-pressure  in,  45,  47,  4%, 

50,59 

capacity  of,  47 
innervation  of,  55 
portal,  55 
pulse  in,  57 
valves  of,  59 


240 


INDEX. 


Velocity  of  blood-flow,  44 
Venosity  of  blood,  influence  of, 
on     cardio-inhibitory 
center,  48 
on    respiratory    center, 

71 

on  vasoconstrictor  cen- 
ter, 51 

Venous  blood,  68 
circulation,  59 
pulse,  59 
Veratrin,  149 
Vermis,  174,  178,  206 
Vertigo,  208 

Vestibular  nerve,  182,  184,  205 
Viscero-inhibitory  nerve-fibers 

of  stomach,  100,  170 
Visceromotor    nerve-fibers    of 

stomach,  100,  170 
Vision,  210 

color,  218,  221 

Visual  area,  185 

judgment,  224 


Visual  purple,  221 

reflexes,  185 
Vitreous  humor,  210 
Vomiting,  103 


WARMTH,  influence  of,  on  res- 
piratory center,  72 
on  vasoconstrictor  center, 

51 

Waste  products,  18 
excretion  of,  127 
of  muscular   metabolism., 

50,  72 

Water,  absorption  of,  95 
excretion  of,  127,  135 
in  diet,  124 
Work,  149 
and  diet,  122 


XANTHIN,  13,  88,  112,  158 


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THE  BEST  nmeriCan  STANDARD 

Illustrated  Dictionary 

Recently  Issued— The  New  (4th)  Edition* 


The  American  Illustrated  Medical  Dictionary.     A  new 

and  complete  dictionary  of  the  terms  used  in  Medicine,  Surgery, 
Dentistry,  Pharmacy,  Chemistry,  and  kindred  branches;  with 
over  100  new  and  elaborate  tables  and  many  handsome  illustra- 
tions. By  W.  A.  NEWMAN  BORLAND,  M.  D.,  Editor  of  "The 
American  Pocket  Medical  Dictionary."  Large  octavo,  nearly 
850  pages,  bound  in  full  flexible  leather.  Price,  $4.50  net;  with 
thumb  index,  $5.00  net. 

Gives  a  Maximum  Amount  of  Matter  in  a  Minimum  Space,  and  at  the 
Lowest  Possible  Cost 

WITH   2000  NEW  TERMS 

The  immediate  success  of  this  work  is  due  to  the  special  features  that 
distinguish  it  from  other  books  of  its  kind.  It  gives  a  maximum  of  matter 
in  a  minimum  space  and  at  the  lowest  possible  cost.  Though  it  is  practi- 
cally unabridged,  yet  by  the  use  of  thin  bible  paper  and  flexible  morocco 
binding  it  is  only  i^  inches  thick.  In  this  new  edition  the  book  has 
been  thoroughly  revised,  and  upward  of  two  thousand  new  terms  have 
been  added,  thus  bringing  the  book  absolutely  up  to  date.  The  book  con- 
tains hundreds  of  terms  not  to  be  found  in  any  other  dictionary,  over  100 
original  tables,  and  many  handsome  illustrations. 


PERSONAL  OPINIONS 


Howard  A.  Kelly,  M.  D., 

Professor  of  Gynecology,  Johns  Hopkins  University,  Baltimore. 

"  Dr.  Borland's  dictionary  is  admirable.     It  is  so  well  gotten  up  and  of  such  conve- 
nient size.     No  errors  have  been  found  in  my  use  of  it." 

J.  Collins  Warren,  M.D., 

Professor  of  Surgery,  Harvard  Medical  School. 

"I  regard  it  as!  a  valuable  aid  to  my  medical  literary  work.     It  is  very  complete  and 
of  convenient  size  to  handle  comfortably.     I  use  it  in  preference  to  any  other." 


EMBRYOLOGY. 


Heisler's 
Text-Book  qf  Embryology 

Recently  Issued— The  New  (3d)  Edition 


A  Text-Book  of  Embryology.  By  JOHN  C.  HEISLER,  M.D., 
Professor  of  Anatomy  in  the  Medico-Chirurgical  College,  Phila- 
delphia. Octavo  volume  of  435  pages,  with  212  illustrations,  32 
of  them  in  colors.  Cloth,  $3.00  net. 

WITH   212   ILLUSTRATIONS.    32   IN   COLORS 

The  fact  of  embryology  having  acquired  in  recent  years  such  great  interest 
in  connection  with  the  teaching  and  with  the  proper  comprehension  of  human 
anatomy,  it  is  of  first  importance  to  the  student  of  medicine  that  a  concise  and 
yet  sufficiently  full  text-book  upon  the  subject  be  available.  The  new  edition 
of  this  work  represents  all  the  latest  advances  recently  made  in  the  science 
of  embryology.  Many  portions  have  been  entirely  rewritten,  and  a  great 
deal  of  new  and  important  matter  added.  A  number  of  new  illustrations 
have  also  been  prepared  which  will  prove  valuable.  Heisler's  Embryology 
has  become  a  standard  work. 


PERSONAL  AND    PRESS   OPINIONS 


G.  Carl  Huber.  M.  D.. 

Professor  of  Histology  and  Embryology,  University  of  Michigan.  Ann  Arbor. 

"  I  find  the  second  edition  of  'A  Text-Book  of  Embryology  '  by  Dr.  Heisler  an  improv.- 
ment  on  the  first.  The  figures  added  increase  greatly  the  value  of  the  work.  I  am  again 
recommending  it  to  our  students." 

William  Wathen,  M.D., 

Professor  of  Obstetrics,  Abdominal  Surgery,  and  Gynecology,  and  Dean,  Kentucky 

School  of  Medicine,  Louisville,  Ky. 

"  It  is  systematic,  scientific,  full  of  simplicity,  and  just  such  a  work  as  a  medical  student 
will  be  able  to  comprehend." 

Birmingham  Medical  Review.  England 

"  We  can  most  confidently  recommend  Dr.  Heisler's  book  to  the  student  of  biology  or 
medicine  for  his  careful  study,  if  his  aim  be  to  acquire  a  sound  and  practical  acquaintance 
with  the  subject  of  embryology." 


SAUNDERS'  BOOKS   ON 


Mallory  and  Wright's 
Pathologic  Technique 

Recently  Issued— Third  Edition,  Enlarged 


Pathologic  Technique.  A  Practical  Manual  for  Workers  in 
Pathologic  Histology,  including  Directions  for  the  Performance 
)f  Autopsies  and  for  Clinical  Diagnosis  by  Laboratory  Methods 
By  FRANK  B.  MALLORY,  M.  D.,  Associate  Professor  of  Pathology, 
harvard  University;  and  JAMES  H.  WRIGHT,  M.  D.,  Director  of 
he  Clinico-Pathologic  Laboratories,  Massachusetts  General  Hos- 
>ital.  Octavo  of  469  pages,  with  138  illustrations.  Cloth, $3.00  net. 

WITH  CHAPTERS  ON  POST-MORTEM  TECHNIQUE  AND 
AUTOPSIES 

In  revising  the  book  for  the  new  edition  the  authors  have  kept  in  view  the 
leeds  of  the  laboratory  worker,  whether  student,  practitioner,  or  pathologist, 
or  a  practical  manual  of  histologic  and  bacteriologic  methods  in  the  study  of 
>athologic  material.  Many  parts  have  been  rewritten,  many  new  methods 
lave  been  added,  and  the  number  of  illustrations  has  been  considerably 
ncreased.  Among  the  many  changes  and  additions  may  be  mentioned  the 
.mplification  of  the  description  of  the  Parasite  of  Actinomycosis  and  the 
nsertion  of  descriptions  of  the  Bacillus  of  Bubonic  Plague,  of  the  Parasite  of 
tfycetoma,  and  Wright's  methods  for  the  cultivation  of  Anaerobic  Bacteria, 
fhere  have  also  been  added  new  staining  methods  for  elastic  tissue  by 
•Veigert,  for  bone  by  Schmorl,  and  for  connective  tissue  by  Mallory. 


PERSONAL  AND   PRESS  OPINIONS 


•Yilliam  H.  Welch,  M.D., 

Professor  of  Pathology,  Johns  Hopkins  University,  Baltimore,  Md. 
"  I  have  been  looking  forward  to  the  publication  of  this  book,  and  I  am  glad  to  say  that 
find  it  a  most  useful  laboratory  and  post-mortem  guide,  full  of  practical  information  and 
veil  up  to  date." 

ioston  Medical  and  Surgical  Journal 

"  This  manual,  since  its  first  appearance,  has  been  recognized  as  the  standard  guide  in 
>athological  technique,  and  has  become  well-nigh  indispensable  to  the  laboratory  worker." 


HISTOLOGY. 


Bohm,  Davidoff,  and 
Huber's  Histology 


A  Text-Book  of  Human  Histology.  Including  Microscopic 
Technic.  By  DR.  A.  A.  BOHM  and  DR.  M.  VON  DAVIDOFF,  of 
Munich,  and  G.  CARL  HUBER,  M.  D.,  Professor  of  Histology 
and  Embryology  in  the  University  of  Michigan,  Ann  Arbor. 
Handsome  octavo  of  528  pages,  with  377  beautiful  original  illus- 
trations. Flexible  cloth,  $3.50  net. 

RECENTLY  ISSUED— SECOND  REVISED  EDITION 

The  work  of  Drs.  Bohm  and  Davidoff  is  well  known  in  the  German  edi- 
tion, and  has  been  considered  one  of  the  most  practically  useful  books  on  the 
subject  of  Human  Histology.  This  American  edition  has  been  in  great  part 
rewritten  and  very  much  enlarged  by  Dr.  Huber,  who  has  also  added  over 
one  hundred  original  illustrations.  Dr.  Huber's  extensive  additions  have 
rendered  the  work  the  most  complete  students'  text-book  on  Histology  in 
existence. 


DrewV 

Invertebrate   Zoology 


A  Laboratory  Manual   of    Invertebrate    Zoology.     By 

GILMAN  A.  DREW,  PH.D.,  Professor  of  Biology  at  the  Univer- 
sity of  Maine.  With  the  aid  of  Members  of  the  Zoological  Staff 
of  Instructors  at  the  Marine  Biological  Laboratory,  Woods  Holl, 
Mass.  i2mo  of  200  pages.  Cloth,  $1.25  net. 

RECENTLY    ISSUED 

The  subject  is  presented  in  a  logical  way,  and  the  type  study  has  been 
followed,  as  this  method  has  been  the  prevailing  one  for  many  years. 

Prof.  Ellison  A.  Smyth,  Jr.,    Virginia  Polytechnic  Institute 


10  SAUNDERS'    BOOKS   ON 

McFarlandfs 
Pathogenic  Bacteria 

The  New(5th)Edition,  Revised 


A  Text-Book  upon  the  Pathogenic  Bacteria.  By  JOSEPH 
MCFARLAND,  M.  D.,  Professor  of  Pathology  and  Bacteriology  in 
the  Medico-Chirurgical  College  of  Philadelphia ;  Pathologist  to 
the  Medico-Chirurgical  Hospital,  Philadelphia,  etc.  Octavo 
volume  of  647  pages,  finely  illustrated.  Cloth,  $3.50  net. 

RECENTLY    ISSUED 

This  book  gives  a  concise  account  of  the  technical  procedures  necessary  in 
the  study  of  bacteriology,  a  brief  description  of  the  life-history  of  the  import- 
ant pathogenic  bacteria,  and  sufficient  description  of  the  pathologic  lesions 
accompanying  the  micro-organism al  invasions  to  give  an  idea  of  the  origin  of 
symptoms  and  the  causes  of  death.  The  illustrations  are  mainly  reproductions 
of  the  best  the  world  affords,  and  are  beautifully  and  accurately  executed. 

The  Lancet,  London 

"  It  is  excellently  adapted  for  practitioners  and  medical  students,  for  whom  it  is  avowedly 
written.  .  .  .  The  descriptions  given  are  accurate  and  readable." 


Hill's 
Histology  and   Organog'raphy 

A  Manual  of  Histology  and  Organography.  By  CHARLES 
HILL,  M.  D.,  Professor  of  Histology  and  Embryology,  North- 
western University,  Chicago.  i2mo  of  463  pages,  with  313 
illustrations.  Flexible  leather,  $2.00  net. 

RECENTLY  ISSUED 

Dr.  Hill's  fifteen  years'  experience  as  a  teacher  of  histology  has  enabled 
him  to  present  a  work  characterized  by  clearness  and  brevity  of  style  and  a 


BACTERIOLOGY  AND  PATHOLOGY.  II 

Eyre's 

Bacteriologic  Technique 

The  Elements  of  Bacteriologic  Technique.  A  Laboratory 
Guide  for  the  Medical,  Dental,  and  Technical  Student.  By  J.  W. 
H.  EYRE,  M.  D.,  F.  R.  S.  Edin.,  Bacteriologist  to  Guy's  Hospital, 
London,  and  Lecturer  on  Bacteriology,  Medical  and  Dental  Schools, 
etc.  Octavo,  375  pages,  with  170  illustrations.  Cloth,  $2.50  net. 

This  book  presents,  concisely  yet  clearly,  the  various  methods  at  present 
in  use  for  the  study  of  bacteria,  and  elucidates  such  points  in  their  life-his- 
tories as  are  debatable  or  still  undetermined.  The  illustrations  are  numerous 
and  practical. 

Medical  News,  New  York 

"Of  the  many  laboratory  guides  constantly  being  issued,  this  book  is  undoubtedly  the 
best  that  has  reached  us." 

Warren's 
Pathology  and  Therapeutics 

Surgical  Pathology  and  Therapeutics.  By  JOHN  COLLINS 
WARREN,  M.  D.,  LL.D.,  F.  R.  C.  S.  (Hon.),  Professor  of  Surgery, 
Harvard  Medical  School.  Octavo,  873  pages,  136  relief  and 
lithographic  illustrations,  33  in  colors.  With  an  Appendix  on 
Scientific  Aids  to  Surgical  Diagnosis,  and  a  series  of  articles  on 
Regional  Bacteriology.  Cloth,  $5.00  net;  Sheep  or  Half  Mo- 
rocco, $6.50  net. 

SECOND   EDITION.  WITH   AN  APPENDIX 

In  the  second  edition  of  this  book  all  the  important  changes  have  been 
embodied  in  a  new  Appendix.  In  addition  to  an  enumeration  of  the  scientific 
aids  to  surgical  diagnosis  there  is  presented  a  series  of  sections  on  regional 
bacteriology,  in  which  are  given  a  description  of  the  flora  of  the  affected 
part,  and  the  general  principles  of  treating  the  affections  they  produce. 

Roswell  Park.  M.  D.. 

In  the  Harvard  Graduate  Magazine. 

"  I  think  it  is  the  most  creditable  book  on  surgical  pathology,  and  the  most  beautiful  medi- 
cal illustration  of  the  bookmakers'  art  that  has  ever  been  issued  from  the  American  press." 


12  SAUNDERS'    BOOKS   ON 

Diirck  arid  Hektoen's 
Special  Pathologic  Histology 

Atlas  and  Epitome  of   Special   Pathologic  Histology. 

By  DR.  H.  DURCK,  of  Munich.  Edited,  with  additions,  by 
LUDVIG  HEKTOEN,  M.  D.,  Professor  of  Pathology,  Rush  Medical 
College,  Chicago.  In  two  parts.  Part  I. — Circulatory,  Respira- 
tory, and  Gastro-intestinal  Tracts.  120  colored  figures  on  62 
plates,  and  158  pages  of  text.  Part  II. — Liver,  Urinary  and 
Sexual  Organs,  Nervous  System,  Skin,  Muscles,  and  Bones.  123 
colored  figures  on  60  plates,  and  192  pages  of  text.  Per  part : 
Cloth,  $3.00  net.  In  Saunders*  Hand-Atlas  Series. 

The  great  value  of  these  plates  is  that  they  represent  in  the  exact  colors 
the  effect  of  the  stains,  which  is  of  such  great  importance  for  the  differentia- 
tion of  tissue.  The  text  portion  of  the  book  is  admirable. 

William  H.  Welch,  M.  D., 

Professor  of  Pathology,  Johns  Hopkins  University,  Baltimore. 

"  I  consider  Diirck's  'Atlas  of  Special  Pathologic  Histology/  edited  by  Hektoen,  a  very 
useful  book  for  students  and  others.  The  plates  are  admirable." 

Sobotta  arid  Huber's 
Human  Histology 

Atlas  and  Epitome  of  Human  Histology  and  Microscopic 
Anatomy.  By  PRIVATDOCENT  DR.  J.  SOBOTTA,  of  Wurzburg. 
Edited,  with  additions,  by  G.  CARL  HUBER,  M.  D.,  Professor  of 
Histology  and  Embryology,  and  Director  of  the  Histological 
Laboratory,  University  of  Michigan,  Ann  Arbor.  With  214 
colored  figures  on  80  plates,  68  text-illustrations,  and  248  pages 
of  text.  Cloth,  $4.50  net.  In  Saunders*  Hand- Atlas  Series. 

Lewellys  F.  Barker,  M.  D., 

Professor  of  the  Principles  and  Practice  of  Medicine,  Johns  Hopkins  University. 

"I  congratulate  you  upon  the  appearance  of  this  volume.  The  illustrations  are 
certainly  very  fine,  and  Dr.  Huber  has  made  important  contributions  to  the  text.  The 
book  should  have  a  large  sale." 


PHYSIOLOGY.  13 


American  Text- Book  of  Physiology 

American  Text-Book  of  Physiology.  In  two  volumes. 
Edited  by  WILLIAM  H.  HOWELL,  PH.  D.,  M.  D.,  Professor  of 
Physiology  in  the  Johns  Hopkins  University,  Baltimore,  Md. 
Two  royal  octavo  volumes  of  about  600  pages  each,  fully  illus- 
trated. Per  volume  :  Cloth,  $3.00  net ;  Sheep  or  Half  Morocco, 
#4-25  net. 

SECOND  EDITION,  REVISED  AND  ENLARGED 

Even  in  the  short  time  that  has  elapsed  since  the  first  edition  of  this 
work  there  has  been  much  progress  in  Physiology,  and  in  this  edition  the 
book  has  been  thoroughly  revised  to  keep  p.ice  with  this  progress.  The 
chapter  upon  the  Central  Nervous  System  has  been  entirely  rewritten.  A 
section  on  Physical  Chemistry  forms  a  valuable  addition,  since  these  views 
are  taking  a  large  part  in  current  discussion  in  physiologic  and  medical 
literature. 

The  Medical  News 

"  The  work  will  stand  as  a  work  of  reference  on  physiology.  To  him  who  desires  to 
know  the  status  of  modern  physiology,  who  expects  to  obtain  suggestions  as  to  further 
physiologic  inquiry,  we  know  of  none  in  English  which  so  eminently  meets  such  a  demand." 

Stewart's  Physiology 

A   Manual   of    Physiology,  with    Practical    Exercises. 

For  Students  and  Practitioners.  By  G.  N.  STEWART,  M.  A., 
M.  D.,  D.  Sc.,  Professor  of  Physiology  in  the  University  of 
Chicago.  Octavo  volume  of  911  pages,  with  395  text-illustra- 
tions and  colored  plates.  Cloth,  #4.00  net. 

RECENTLY  ISSUED— NEW  (5th)  EDITION 

This  work  is  written  in  a  plain  and  attractive  style  that  renders  it  particu- 
larly suited  to  the  needs  of  students.  The  systematic  portion  is  so  treated  that 
it  can  be  used  independently  of  the  practical  exercises,  which  constitute  an 
important  feature  of  the  book.  In  the  present  edition  a  considerable  amount 
of  m-w  matter  has  been  added,  especially  to  the  chapters  on  Blood,  Digestion, 
and  the  Central  Nervous  System. 

Philadelphia  Medical  Journal 

"  Those  familiar  with  the  attainments  of  Prof.  Stewart  as  an  original  investigator,  as  a 
teacher  and  a  writer,  need  no  assurance  that  in  this  volume  he  has  presented  in  a  ter»e, 
concise,  accurate  manner  the  essential  and  best  established  facts  of  physiology  in  a  most 
attractive  manner." 


14  SAUNDERS'    fOOJfS    ON 

Levy  and  Klemperer's 
Clinical   Bacteriology 

The  Elements  of  Clinical  Bacteriology.  By  DRS.  ERNST 
LEVY  and  FELIX  KLEMPERER,  of  the  University  of  Strasburg- 
Translated  and  edited  by  AUGUSTUS  A.  ESHNER,  M.  D.,  Pro- 
fessor of  Clinical  Medicine,  Philadelphia  Polyclinic.  Octavo 
volume  of  440  pages,  fully  illustrated.  Cloth,  $2.50  net. 

Lehmann,  Neumann,  and 
Weaver's  Bacteriology 

Atlas  and  Epitome  of  Bacteriology  :  INCLUDING  A  TEXT- 
BOOK OF  SPECIAL  BACTERIOLOGIC  DIAGNOSIS.  By  PROF.  DR. 
K.  B.  LEHMANN  and  DR.  R.  O.  NEUMANN,  of  Wiirzburg.  From 
the  Second  Revised  and  Enlarged  German  Edition.  Edited, 
with  additions,  by  G.  H.  WEAVER,  M.  D.,  Assistant  Professor 
of  Pathology  and  Bacteriology,  Rush  Medical  College,  Chicago. 
In  two  parts.  Part  I. — 632  colored  figures  on  69  lithographic 
plates.  Part  II. — 511  pages  of  text,  illustrated.  Per  part: 
Cloth,  $2.50  net.  In  Saunders'  Hand-Atlas  Series. 

Lewis'  Anatomy  and  Physiology 

Anatomy  and  Physiology  for  Nurses.  By  LEROY 
LEWIS,  M.  D. ,  Surgeon  to  and  Lecturer  on  Anatomy  and  Physi- 
ology for  Nurses  at  the  Lewis  Hospital,  Bay  City,  Michigan. 
i2mo  of  317  pages,  with  146  illustrations.  Cloth,  $1.75  net, 

RECENTLY    ISSUED 

Nurses  Journal  of  the  Pacific  Coast 

"  It  is  not  in  any  sense  rudimentary,  but  comprehensive  in  its  treatment  of  the  subjects 
in  hand." 


PATHOLOGY,  BACTERIOLOGY,  AND   PHYSIOLOGY.      15 


Tumors  Second  Revised  Edition 

PATHOLOGY  AND  SURGICAL  TREATMENT  OF  TUMORS.  By  NICHOLAS 
SENN,  M.  D.,  PH.  D.,  LL.D.,  Professor  of  Surgery,  Rush  Medical  Col- 
lege, Chicago.  Handsome  octavo,  718  pages,  with  478  engravings, 
including  12  full-page  colored  plates.  Cloth,  #5.00  net ;  Sheep  or 
Half  Morocco,  $6.50  net. 

"  The  most  exhaustive  of  any  recent  book  in  English  on  this  subject.  It  is  well 
illustrated,  and  will  doubtless  remain  as  the  principal  monograph  on  the  subject  in 
our  language  for  some  years."— Journat  of  the  American  Medical  Association. 

Stoney's  Bacteriology  and  Technic 

BACTERIOLOGY  AND  SURGICAL  TECHNIC  FOR  NURSES.  BY  EMILY 
M.  A.  STONEY,  Superintendent  of  the  Training  School  for  Nurses  at  the 
Carney  Hospital,  South  Boston,  Mass.  Revised  by  FREDERIC  R.  GRIF- 
FITH, M.D.,  Surgeon,  New  York.  I2mo  of  278  pages,  profusely  illus- 
trated. Cloth,  $1.50  net. 

"  These  subjects  are  treated  most  accurately  and  up  to  date,  without  the  super- 
fluous reading  which  is  so  often  employed.  .  .  .  Nurses  will  find  this  book  of  the 
greatest  value." —  The  Trained  Nurse  and  Hospital  Review. 

Clarkson's  Histology 

A  TEXT-BOOK  OF  HISTOLOGY.  Descriptive  and  Practical.  For  the 
Use  of  Students.  By  ARTHUR  CLARKSON,  M.  B.,  C.  M.  Edin.,  for- 
merly Demonstrator  of  Physiology  in  the  Owen's  College,  Manchester, 
England.  Octavo,  554  pages,  with  174  colored  original  illustrations. 
Cloth,  $4.00  net. 

"  The  volume  in  the  hands  of  students  will  greatly  aid  in  the  comprehension  of  a 
subject  which  in  most  instances  is  found  rather  difficult.  .  .  .  The  work  must  be  con- 
sidered a  valuable  addition  to  the  list  of  available  text-bboks,  and  is  to  be  highly 
recommended." — New  York  Medical  Journal. 

Gorham's  Bacteriology 

A  LABORATORY  COURSE  IN  BACTERIOLOGY.  For  the  Use  of  Medical, 
Agricultural,  and  Industrial  Students.  By  FREDERIC  P.  GORHAM, 
A.  M.,  Associate  Professor  of  Biology  in  Brown  University,  Providence, 
R.  I.,  etc.  I2mo  of  192  pages,  with  97  illustrations.  Cloth,  $1.25  net. 

"  One  of  the  best  students'  laboratory  guides  to  the  study  of  bacteriology  on  the 
market.  .  .  .  The  technic  is  thoroughly  modern  and  amply  sufficient  for  all  practical 
purposes."— American  Journal  of  the  Medical  Sciences. 

.  Recently  Issued 

Raymond  s  Physiology  New  od)  Edition 

HUMAN  PHYSIOLOGY.  By  JOSEPH  H.  RAYMOND  A.  M..  M.  D  .Pro- 
fessor of  Physiology  and  Hygiene,  Long  Island  College  Hospital,  New 
York.  Octavo  of  685  pages,  with  444  illustrations.  Cloth,  $3.  'O  net. 

"The  book  is  well  gotten  up  and  well  printed,  and  may  be  regarded  as  a  trust- 
worthy guide  for  the  student  and  a  useful  work  of  reference  for  the  genera  practi- 
tioner. The  illustrations  are  numerous  and  are  well  executed.'  -  The  Lancet,  London. 


16     BACTERIOLOGY,  PHYSIOLOGY,  AND  HISTOLOGY. 

Ball's    Bacteriology  Recently  Issued—  Fifth  Edition,  Revised 

ESSENTIALS  OF  BACTERIOLOGY  :  being  a  concise  and  systematic  intro- 
duction to  the  Study  of  Micro-organisms.  By  M.  V.  BALL,  M.  D.,  late 
Bacteriologist  to  St.  Agnes'  Hospital,  Philadelphia.  I2mo  of  236  pages, 
with  96  illustrations,  some  in  colors,  and  5  plates.  Cloth,  $1.00  net. 
In  Saunders1  Question-  Compend  Series. 

"  The  technic  with  regard  to  media,  staining,  mounting,  and  the  like  is  culled  from 
the  latest  authoritative  works."  —  77ia  Medical  Times,  New  York. 


Budgett's  Physiology 

ESSENTIALS  OF  PHYSIOLOGY.  Prepared  especially  for  Students  of 
Medicine,  and  arranged  with  questions  following  each  chapter.  By 
SIDNEY  P.  BUDGETT,  M.  D.,  Professor  of  Physiology,  Medical  Depart- 
ment of  Washington  University,  St.  Louis.  i6mo  volume  of  245  pages, 
finely  illustrated  with  many  full-page  half-tones.  Cloth,  $1.00  net.  In 
Saunders''  Question-  Compend  Series. 

"  He  has  an  excellent  conception  of  his  subject  ...  It  is  one  of  the  most  satisfac- 
tory books  of  this  c\a.^.—  University  of  Pennsylvania  Medical  Bulletin. 

Recently  Issued 

Leroy  s  Histology  New  (3d)  Edition 

ESSENTIALS  OF  HISTOLOGY.  By  Louis  LEROY,  M.  D.,  Professor  of 
Histology  and  Pathology,  Vanderbilt  University,  Nashville,  Tennessee. 
I2mo,  275  pages,  with  92  original  illustrations.  Cloth,  $i.co  net.  In 
Saunders1  Question-  Compend  Series. 

"  The  work  in  its  present  form  stands  as  a  model  of  what  a  student's  aid  should  be  ; 
and  we  unhesitatingly  say  that  the  practitioner  as  well  would  find  a  glance  through 
the  book  of  lasting  benefit  "—The  Medical  World,  Philadelphia. 

Bastin's  Botany 

LABORATORY  EXERCISES  IN  BOTANY.  By  the  late  EDSON  S.  BASTIN, 
M.  A.  Octavo,  536  pages,  with  87  plates.  Cloth,  $2.00  net. 

Barton  and  Wells'  Medical  Thesaurus 

A  THESAURUS  OF  MEDICAL  WORDS  AND  PHRASES.  By  WILFRED  M. 
BARTON,  M.  D.,  Assistant  Professor  of  Materia  Medica  and  Therapeu- 
tics ;  and  WALTER  A.  WELLS,  M.  D.,  Demonstrator  of  Laryngology, 
Georgetown  University,  Washington,  D.  C.  I2mo,  534  pages.  Flexible 
leather,  $2.50  net. 

.  Fifth  Edition,  Revised 

American  Pocket  Dictionary  Recently  issued 

AMERICAN  POCKET  MEDICAL  DICTIONARY.  Edited  by  W.  A. 
NEWMAN  DORLAND,  M.  D.,  Assistant  Obstetrician  to  the  Hospital  ot 
the  University  of  Pennsylvania.  Containing  the  pronunciation  and  < 
nition  of  the  principal  words  used  in  medicine  and  kindred  sciences, 
with  64  extensive  tables.  Handsomely  bound  in  flexible  leather,  with 
gold  edges,  $1.00  net;  with  patent  thumb  index,  $1.25  net. 

"  I  can  recommend  it  to  our  students  without  reserve."—  J.  H.  HOLLAND,  M.  D,, 
of  the  Jefferson  Medical  College,  Philadelphia. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 


This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


MOV     5  1S5S 

OTTOTW 

DQT191960 

„'-,-« 

DEC  Ifi  19Rn 

UL.U     J-  O 

V9 

MAR'^O^e? 

OCT  31  1964 

^^ 

General  Library 
University  of  California 

R*rlral«v 

LD  21-100m-6,'56 
(B9311slO)476 

' 


